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Differences Between: [Versions 310 and 401] [Versions 311 and 401] [Versions 39 and 401] [Versions 400 and 401] [Versions 401 and 402] [Versions 401 and 403]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  /**
  18   * Abstract database driver class.
  19   *
  20   * @package    core_dml
  21   * @copyright  2008 Petr Skoda (http://skodak.org)
  22   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  23   */
  24  
  25  defined('MOODLE_INTERNAL') || die();
  26  
  27  require_once (__DIR__.'/database_column_info.php');
  28  require_once (__DIR__.'/moodle_recordset.php');
  29  require_once (__DIR__.'/moodle_transaction.php');
  30  
  31  /** SQL_PARAMS_NAMED - Bitmask, indicates :name type parameters are supported by db backend. */
  32  define('SQL_PARAMS_NAMED', 1);
  33  
  34  /** SQL_PARAMS_QM - Bitmask, indicates ? type parameters are supported by db backend. */
  35  define('SQL_PARAMS_QM', 2);
  36  
  37  /** SQL_PARAMS_DOLLAR - Bitmask, indicates $1, $2, ... type parameters are supported by db backend. */
  38  define('SQL_PARAMS_DOLLAR', 4);
  39  
  40  /** SQL_QUERY_SELECT - Normal select query, reading only. */
  41  define('SQL_QUERY_SELECT', 1);
  42  
  43  /** SQL_QUERY_INSERT - Insert select query, writing. */
  44  define('SQL_QUERY_INSERT', 2);
  45  
  46  /** SQL_QUERY_UPDATE - Update select query, writing. */
  47  define('SQL_QUERY_UPDATE', 3);
  48  
  49  /** SQL_QUERY_STRUCTURE - Query changing db structure, writing. */
  50  define('SQL_QUERY_STRUCTURE', 4);
  51  
  52  /** SQL_QUERY_AUX - Auxiliary query done by driver, setting connection config, getting table info, etc. */
  53  define('SQL_QUERY_AUX', 5);
  54  
  55  /** SQL_QUERY_AUX_READONLY - Auxiliary query that can be done using the readonly connection:
  56   * database parameters, table/index/column lists, if not within transaction/ddl. */
  57  define('SQL_QUERY_AUX_READONLY', 6);
  58  
  59  /**
  60   * Abstract class representing moodle database interface.
  61   * @link https://moodledev.io/docs/apis/core/dml/ddl
  62   *
  63   * @package    core_dml
  64   * @copyright  2008 Petr Skoda (http://skodak.org)
  65   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  66   */
  67  abstract class moodle_database {
  68  
  69      /** @var database_manager db manager which allows db structure modifications. */
  70      protected $database_manager;
  71      /** @var moodle_temptables temptables manager to provide cross-db support for temp tables. */
  72      protected $temptables;
  73      /** @var array Cache of table info. */
  74      protected $tables  = null;
  75  
  76      // db connection options
  77      /** @var string db host name. */
  78      protected $dbhost;
  79      /** @var string db host user. */
  80      protected $dbuser;
  81      /** @var string db host password. */
  82      protected $dbpass;
  83      /** @var string db name. */
  84      protected $dbname;
  85      /** @var string Prefix added to table names. */
  86      protected $prefix;
  87  
  88      /** @var array Database or driver specific options, such as sockets or TCP/IP db connections. */
  89      protected $dboptions;
  90  
  91      /** @var bool True means non-moodle external database used.*/
  92      protected $external;
  93  
  94      /** @var int The database reads (performance counter).*/
  95      protected $reads = 0;
  96      /** @var int The database writes (performance counter).*/
  97      protected $writes = 0;
  98      /** @var float Time queries took to finish, seconds with microseconds.*/
  99      protected $queriestime = 0;
 100  
 101      /** @var int Debug level. */
 102      protected $debug  = 0;
 103  
 104      /** @var string Last used query sql. */
 105      protected $last_sql;
 106      /** @var array Last query parameters. */
 107      protected $last_params;
 108      /** @var int Last query type. */
 109      protected $last_type;
 110      /** @var string Last extra info. */
 111      protected $last_extrainfo;
 112      /** @var float Last time in seconds with millisecond precision. */
 113      protected $last_time;
 114      /** @var bool Flag indicating logging of query in progress. This helps prevent infinite loops. */
 115      protected $loggingquery = false;
 116  
 117      /** @var bool True if the db is used for db sessions. */
 118      protected $used_for_db_sessions = false;
 119  
 120      /** @var array Array containing open transactions. */
 121      protected $transactions = array();
 122      /** @var bool Flag used to force rollback of all current transactions. */
 123      private $force_rollback = false;
 124  
 125      /** @var string MD5 of settings used for connection. Used by MUC as an identifier. */
 126      private $settingshash;
 127  
 128      /** @var cache_application for column info */
 129      protected $metacache;
 130  
 131      /** @var cache_request for column info on temp tables */
 132      protected $metacachetemp;
 133  
 134      /** @var bool flag marking database instance as disposed */
 135      protected $disposed;
 136  
 137      /**
 138       * @var int internal temporary variable used to fix params. Its used by {@link _fix_sql_params_dollar_callback()}.
 139       */
 140      private $fix_sql_params_i;
 141      /**
 142       * @var int internal temporary variable used to guarantee unique parameters in each request. Its used by {@link get_in_or_equal()}.
 143       */
 144      protected $inorequaluniqueindex = 1;
 145  
 146      /**
 147       * @var boolean variable use to temporarily disable logging.
 148       */
 149      protected $skiplogging = false;
 150  
 151      /**
 152       * Constructor - Instantiates the database, specifying if it's external (connect to other systems) or not (Moodle DB).
 153       *              Note that this affects the decision of whether prefix checks must be performed or not.
 154       * @param bool $external True means that an external database is used.
 155       */
 156      public function __construct($external=false) {
 157          $this->external  = $external;
 158      }
 159  
 160      /**
 161       * Destructor - cleans up and flushes everything needed.
 162       */
 163      public function __destruct() {
 164          $this->dispose();
 165      }
 166  
 167      /**
 168       * Detects if all needed PHP stuff are installed for DB connectivity.
 169       * Note: can be used before connect()
 170       * @return mixed True if requirements are met, otherwise a string if something isn't installed.
 171       */
 172      public abstract function driver_installed();
 173  
 174      /**
 175       * Returns database table prefix
 176       * Note: can be used before connect()
 177       * @return string The prefix used in the database.
 178       */
 179      public function get_prefix() {
 180          return $this->prefix;
 181      }
 182  
 183      /**
 184       * Loads and returns a database instance with the specified type and library.
 185       *
 186       * The loaded class is within lib/dml directory and of the form: $type.'_'.$library.'_moodle_database'
 187       *
 188       * @param string $type Database driver's type. (eg: mysqli, pgsql, mssql, sqldrv, oci, etc.)
 189       * @param string $library Database driver's library (native, pdo, etc.)
 190       * @param bool $external True if this is an external database.
 191       * @return moodle_database driver object or null if error, for example of driver object see {@link mysqli_native_moodle_database}
 192       */
 193      public static function get_driver_instance($type, $library, $external = false) {
 194          global $CFG;
 195  
 196          $classname = $type.'_'.$library.'_moodle_database';
 197          $libfile   = "$CFG->libdir/dml/$classname.php";
 198  
 199          if (!file_exists($libfile)) {
 200              return null;
 201          }
 202  
 203          require_once($libfile);
 204          return new $classname($external);
 205      }
 206  
 207      /**
 208       * Returns the database vendor.
 209       * Note: can be used before connect()
 210       * @return string The db vendor name, usually the same as db family name.
 211       */
 212      public function get_dbvendor() {
 213          return $this->get_dbfamily();
 214      }
 215  
 216      /**
 217       * Returns the database family type. (This sort of describes the SQL 'dialect')
 218       * Note: can be used before connect()
 219       * @return string The db family name (mysql, postgres, mssql, oracle, etc.)
 220       */
 221      public abstract function get_dbfamily();
 222  
 223      /**
 224       * Returns a more specific database driver type
 225       * Note: can be used before connect()
 226       * @return string The db type mysqli, pgsql, oci, mssql, sqlsrv
 227       */
 228      protected abstract function get_dbtype();
 229  
 230      /**
 231       * Returns the general database library name
 232       * Note: can be used before connect()
 233       * @return string The db library type -  pdo, native etc.
 234       */
 235      protected abstract function get_dblibrary();
 236  
 237      /**
 238       * Returns the localised database type name
 239       * Note: can be used before connect()
 240       * @return string
 241       */
 242      public abstract function get_name();
 243  
 244      /**
 245       * Returns the localised database configuration help.
 246       * Note: can be used before connect()
 247       * @return string
 248       */
 249      public abstract function get_configuration_help();
 250  
 251      /**
 252       * Returns the localised database description
 253       * Note: can be used before connect()
 254       * @deprecated since 2.6
 255       * @return string
 256       */
 257      public function get_configuration_hints() {
 258          debugging('$DB->get_configuration_hints() method is deprecated, use $DB->get_configuration_help() instead');
 259          return $this->get_configuration_help();
 260      }
 261  
 262      /**
 263       * Returns the db related part of config.php
 264       * @return stdClass
 265       */
 266      public function export_dbconfig() {
 267          $cfg = new stdClass();
 268          $cfg->dbtype    = $this->get_dbtype();
 269          $cfg->dblibrary = $this->get_dblibrary();
 270          $cfg->dbhost    = $this->dbhost;
 271          $cfg->dbname    = $this->dbname;
 272          $cfg->dbuser    = $this->dbuser;
 273          $cfg->dbpass    = $this->dbpass;
 274          $cfg->prefix    = $this->prefix;
 275          if ($this->dboptions) {
 276              $cfg->dboptions = $this->dboptions;
 277          }
 278  
 279          return $cfg;
 280      }
 281  
 282      /**
 283       * Diagnose database and tables, this function is used
 284       * to verify database and driver settings, db engine types, etc.
 285       *
 286       * @return string null means everything ok, string means problem found.
 287       */
 288      public function diagnose() {
 289          return null;
 290      }
 291  
 292      /**
 293       * Connects to the database.
 294       * Must be called before other methods.
 295       * @param string $dbhost The database host.
 296       * @param string $dbuser The database user to connect as.
 297       * @param string $dbpass The password to use when connecting to the database.
 298       * @param string $dbname The name of the database being connected to.
 299       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 300       * @param array $dboptions driver specific options
 301       * @return bool true
 302       * @throws dml_connection_exception if error
 303       */
 304      public abstract function connect($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null);
 305  
 306      /**
 307       * Store various database settings
 308       * @param string $dbhost The database host.
 309       * @param string $dbuser The database user to connect as.
 310       * @param string $dbpass The password to use when connecting to the database.
 311       * @param string $dbname The name of the database being connected to.
 312       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 313       * @param array $dboptions driver specific options
 314       * @return void
 315       */
 316      protected function store_settings($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null) {
 317          $this->dbhost    = $dbhost;
 318          $this->dbuser    = $dbuser;
 319          $this->dbpass    = $dbpass;
 320          $this->dbname    = $dbname;
 321          $this->prefix    = $prefix;
 322          $this->dboptions = (array)$dboptions;
 323      }
 324  
 325      /**
 326       * Returns a hash for the settings used during connection.
 327       *
 328       * If not already requested it is generated and stored in a private property.
 329       *
 330       * @return string
 331       */
 332      protected function get_settings_hash() {
 333          if (empty($this->settingshash)) {
 334              $this->settingshash = md5($this->dbhost . $this->dbuser . $this->dbname . $this->prefix);
 335          }
 336          return $this->settingshash;
 337      }
 338  
 339      /**
 340       * Handle the creation and caching of the databasemeta information for all databases.
 341       *
 342       * @return cache_application The databasemeta cachestore to complete operations on.
 343       */
 344      protected function get_metacache() {
 345          if (!isset($this->metacache)) {
 346              $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 347              $this->metacache = cache::make('core', 'databasemeta', $properties);
 348          }
 349          return $this->metacache;
 350      }
 351  
 352      /**
 353       * Handle the creation and caching of the temporary tables.
 354       *
 355       * @return cache_application The temp_tables cachestore to complete operations on.
 356       */
 357      protected function get_temp_tables_cache() {
 358          if (!isset($this->metacachetemp)) {
 359              // Using connection data to prevent collisions when using the same temp table name with different db connections.
 360              $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 361              $this->metacachetemp = cache::make('core', 'temp_tables', $properties);
 362          }
 363          return $this->metacachetemp;
 364      }
 365  
 366      /**
 367       * Attempt to create the database
 368       * @param string $dbhost The database host.
 369       * @param string $dbuser The database user to connect as.
 370       * @param string $dbpass The password to use when connecting to the database.
 371       * @param string $dbname The name of the database being connected to.
 372       * @param array $dboptions An array of optional database options (eg: dbport)
 373       *
 374       * @return bool success True for successful connection. False otherwise.
 375       */
 376      public function create_database($dbhost, $dbuser, $dbpass, $dbname, array $dboptions=null) {
 377          return false;
 378      }
 379  
 380      /**
 381       * Returns transaction trace for debugging purposes.
 382       * @private to be used by core only
 383       * @return array or null if not in transaction.
 384       */
 385      public function get_transaction_start_backtrace() {
 386          if (!$this->transactions) {
 387              return null;
 388          }
 389          $lowesttransaction = end($this->transactions);
 390          return $lowesttransaction->get_backtrace();
 391      }
 392  
 393      /**
 394       * Closes the database connection and releases all resources
 395       * and memory (especially circular memory references).
 396       * Do NOT use connect() again, create a new instance if needed.
 397       * @return void
 398       */
 399      public function dispose() {
 400          if ($this->disposed) {
 401              return;
 402          }
 403          $this->disposed = true;
 404          if ($this->transactions) {
 405              $this->force_transaction_rollback();
 406          }
 407  
 408          if ($this->temptables) {
 409              $this->temptables->dispose();
 410              $this->temptables = null;
 411          }
 412          if ($this->database_manager) {
 413              $this->database_manager->dispose();
 414              $this->database_manager = null;
 415          }
 416          $this->tables  = null;
 417      }
 418  
 419      /**
 420       * This should be called before each db query.
 421       *
 422       * @param string $sql The query string.
 423       * @param array|null $params An array of parameters.
 424       * @param int $type The type of query ( SQL_QUERY_SELECT | SQL_QUERY_AUX_READONLY | SQL_QUERY_AUX |
 425       *                  SQL_QUERY_INSERT | SQL_QUERY_UPDATE | SQL_QUERY_STRUCTURE ).
 426       * @param mixed $extrainfo This is here for any driver specific extra information.
 427       * @return void
 428       */
 429      protected function query_start($sql, ?array $params, $type, $extrainfo=null) {
 430          if ($this->loggingquery) {
 431              return;
 432          }
 433          $this->last_sql       = $sql;
 434          $this->last_params    = $params;
 435          $this->last_type      = $type;
 436          $this->last_extrainfo = $extrainfo;
 437          $this->last_time      = microtime(true);
 438  
 439          switch ($type) {
 440              case SQL_QUERY_SELECT:
 441              case SQL_QUERY_AUX:
 442              case SQL_QUERY_AUX_READONLY:
 443                  $this->reads++;
 444                  break;
 445              case SQL_QUERY_INSERT:
 446              case SQL_QUERY_UPDATE:
 447              case SQL_QUERY_STRUCTURE:
 448                  $this->writes++;
 449              default:
 450                  if ((PHPUNIT_TEST) || (defined('BEHAT_TEST') && BEHAT_TEST) ||
 451                      defined('BEHAT_SITE_RUNNING')) {
 452  
 453                      // Set list of tables that are updated.
 454                      require_once (__DIR__.'/../testing/classes/util.php');
 455                      testing_util::set_table_modified_by_sql($sql);
 456                  }
 457          }
 458  
 459          $this->print_debug($sql, $params);
 460      }
 461  
 462      /**
 463       * This should be called immediately after each db query. It does a clean up of resources.
 464       * It also throws exceptions if the sql that ran produced errors.
 465       * @param mixed $result The db specific result obtained from running a query.
 466       * @throws dml_read_exception | dml_write_exception | ddl_change_structure_exception
 467       * @return void
 468       */
 469      protected function query_end($result) {
 470          if ($this->loggingquery) {
 471              return;
 472          }
 473          if ($result !== false) {
 474              $this->query_log();
 475              // free memory
 476              $this->last_sql    = null;
 477              $this->last_params = null;
 478              $this->print_debug_time();
 479              return;
 480          }
 481  
 482          // remember current info, log queries may alter it
 483          $type   = $this->last_type;
 484          $sql    = $this->last_sql;
 485          $params = $this->last_params;
 486          $error  = $this->get_last_error();
 487  
 488          $this->query_log($error);
 489  
 490          switch ($type) {
 491              case SQL_QUERY_SELECT:
 492              case SQL_QUERY_AUX:
 493              case SQL_QUERY_AUX_READONLY:
 494                  throw new dml_read_exception($error, $sql, $params);
 495              case SQL_QUERY_INSERT:
 496              case SQL_QUERY_UPDATE:
 497                  throw new dml_write_exception($error, $sql, $params);
 498              case SQL_QUERY_STRUCTURE:
 499                  $this->get_manager(); // includes ddl exceptions classes ;-)
 500                  throw new ddl_change_structure_exception($error, $sql);
 501          }
 502      }
 503  
 504      /**
 505       * This logs the last query based on 'logall', 'logslow' and 'logerrors' options configured via $CFG->dboptions .
 506       * @param string|bool $error or false if not error
 507       * @return void
 508       */
 509      public function query_log($error=false) {
 510          // Logging disabled by the driver.
 511          if ($this->skiplogging) {
 512              return;
 513          }
 514  
 515          $logall    = !empty($this->dboptions['logall']);
 516          $logslow   = !empty($this->dboptions['logslow']) ? $this->dboptions['logslow'] : false;
 517          $logerrors = !empty($this->dboptions['logerrors']);
 518          $iserror   = ($error !== false);
 519  
 520          $time = $this->query_time();
 521  
 522          // Will be shown or not depending on MDL_PERF values rather than in dboptions['log*].
 523          $this->queriestime = $this->queriestime + $time;
 524  
 525          if ($logall or ($logslow and ($logslow < ($time+0.00001))) or ($iserror and $logerrors)) {
 526              $this->loggingquery = true;
 527              try {
 528                  $backtrace = debug_backtrace();
 529                  if ($backtrace) {
 530                      //remove query_log()
 531                      array_shift($backtrace);
 532                  }
 533                  if ($backtrace) {
 534                      //remove query_end()
 535                      array_shift($backtrace);
 536                  }
 537                  $log = new stdClass();
 538                  $log->qtype      = $this->last_type;
 539                  $log->sqltext    = $this->last_sql;
 540                  $log->sqlparams  = var_export((array)$this->last_params, true);
 541                  $log->error      = (int)$iserror;
 542                  $log->info       = $iserror ? $error : null;
 543                  $log->backtrace  = format_backtrace($backtrace, true);
 544                  $log->exectime   = $time;
 545                  $log->timelogged = time();
 546                  $this->insert_record('log_queries', $log);
 547              } catch (Exception $ignored) {
 548              }
 549              $this->loggingquery = false;
 550          }
 551      }
 552  
 553      /**
 554       * Disable logging temporarily.
 555       */
 556      protected function query_log_prevent() {
 557          $this->skiplogging = true;
 558      }
 559  
 560      /**
 561       * Restore old logging behavior.
 562       */
 563      protected function query_log_allow() {
 564          $this->skiplogging = false;
 565      }
 566  
 567      /**
 568       * Returns the time elapsed since the query started.
 569       * @return float Seconds with microseconds
 570       */
 571      protected function query_time() {
 572          return microtime(true) - $this->last_time;
 573      }
 574  
 575      /**
 576       * Returns database server info array
 577       * @return array Array containing 'description' and 'version' at least.
 578       */
 579      public abstract function get_server_info();
 580  
 581      /**
 582       * Returns supported query parameter types
 583       * @return int bitmask of accepted SQL_PARAMS_*
 584       */
 585      protected abstract function allowed_param_types();
 586  
 587      /**
 588       * Returns the last error reported by the database engine.
 589       * @return string The error message.
 590       */
 591      public abstract function get_last_error();
 592  
 593      /**
 594       * Prints sql debug info
 595       * @param string $sql The query which is being debugged.
 596       * @param array $params The query parameters. (optional)
 597       * @param mixed $obj The library specific object. (optional)
 598       * @return void
 599       */
 600      protected function print_debug($sql, array $params=null, $obj=null) {
 601          if (!$this->get_debug()) {
 602              return;
 603          }
 604          if (CLI_SCRIPT) {
 605              $separator = "--------------------------------\n";
 606              echo $separator;
 607              echo "{$sql}\n";
 608              if (!is_null($params)) {
 609                  echo "[" . var_export($params, true) . "]\n";
 610              }
 611              echo $separator;
 612          } else if (AJAX_SCRIPT) {
 613              $separator = "--------------------------------";
 614              error_log($separator);
 615              error_log($sql);
 616              if (!is_null($params)) {
 617                  error_log("[" . var_export($params, true) . "]");
 618              }
 619              error_log($separator);
 620          } else {
 621              $separator = "<hr />\n";
 622              echo $separator;
 623              echo s($sql) . "\n";
 624              if (!is_null($params)) {
 625                  echo "[" . s(var_export($params, true)) . "]\n";
 626              }
 627              echo $separator;
 628          }
 629      }
 630  
 631      /**
 632       * Prints the time a query took to run.
 633       * @return void
 634       */
 635      protected function print_debug_time() {
 636          if (!$this->get_debug()) {
 637              return;
 638          }
 639          $time = $this->query_time();
 640          $message = "Query took: {$time} seconds.\n";
 641          if (CLI_SCRIPT) {
 642              echo $message;
 643              echo "--------------------------------\n";
 644          } else if (AJAX_SCRIPT) {
 645              error_log($message);
 646              error_log("--------------------------------");
 647          } else {
 648              echo s($message);
 649              echo "<hr />\n";
 650          }
 651      }
 652  
 653      /**
 654       * Returns the SQL WHERE conditions.
 655       * @param string $table The table name that these conditions will be validated against.
 656       * @param array $conditions The conditions to build the where clause. (must not contain numeric indexes)
 657       * @throws dml_exception
 658       * @return array An array list containing sql 'where' part and 'params'.
 659       */
 660      protected function where_clause($table, array $conditions=null) {
 661          // We accept nulls in conditions
 662          $conditions = is_null($conditions) ? array() : $conditions;
 663  
 664          if (empty($conditions)) {
 665              return array('', array());
 666          }
 667  
 668          // Some checks performed under debugging only
 669          if (debugging()) {
 670              $columns = $this->get_columns($table);
 671              if (empty($columns)) {
 672                  // no supported columns means most probably table does not exist
 673                  throw new dml_exception('ddltablenotexist', $table);
 674              }
 675              foreach ($conditions as $key=>$value) {
 676                  if (!isset($columns[$key])) {
 677                      $a = new stdClass();
 678                      $a->fieldname = $key;
 679                      $a->tablename = $table;
 680                      throw new dml_exception('ddlfieldnotexist', $a);
 681                  }
 682                  $column = $columns[$key];
 683                  if ($column->meta_type == 'X') {
 684                      //ok so the column is a text column. sorry no text columns in the where clause conditions
 685                      throw new dml_exception('textconditionsnotallowed', $conditions);
 686                  }
 687              }
 688          }
 689  
 690          $allowed_types = $this->allowed_param_types();
 691          $where = array();
 692          $params = array();
 693  
 694          foreach ($conditions as $key=>$value) {
 695              if (is_int($key)) {
 696                  throw new dml_exception('invalidnumkey');
 697              }
 698              if (is_null($value)) {
 699                  $where[] = "$key IS NULL";
 700              } else {
 701                  if ($allowed_types & SQL_PARAMS_NAMED) {
 702                      // Need to verify key names because they can contain, originally,
 703                      // spaces and other forbidden chars when using sql_xxx() functions and friends.
 704                      $normkey = trim(preg_replace('/[^a-zA-Z0-9_-]/', '_', $key), '-_');
 705                      if ($normkey !== $key) {
 706                          debugging('Invalid key found in the conditions array.');
 707                      }
 708                      $where[] = "$key = :$normkey";
 709                      $params[$normkey] = $value;
 710                  } else {
 711                      $where[] = "$key = ?";
 712                      $params[] = $value;
 713                  }
 714              }
 715          }
 716          $where = implode(" AND ", $where);
 717          return array($where, $params);
 718      }
 719  
 720      /**
 721       * Returns SQL WHERE conditions for the ..._list group of methods.
 722       *
 723       * @param string $field the name of a field.
 724       * @param array $values the values field might take.
 725       * @return array An array containing sql 'where' part and 'params'
 726       */
 727      protected function where_clause_list($field, array $values) {
 728          if (empty($values)) {
 729              return array("1 = 2", array()); // Fake condition, won't return rows ever. MDL-17645
 730          }
 731  
 732          // Note: Do not use get_in_or_equal() because it can not deal with bools and nulls.
 733  
 734          $params = array();
 735          $select = "";
 736          $values = (array)$values;
 737          foreach ($values as $value) {
 738              if (is_bool($value)) {
 739                  $value = (int)$value;
 740              }
 741              if (is_null($value)) {
 742                  $select = "$field IS NULL";
 743              } else {
 744                  $params[] = $value;
 745              }
 746          }
 747          if ($params) {
 748              if ($select !== "") {
 749                  $select = "$select OR ";
 750              }
 751              $count = count($params);
 752              if ($count == 1) {
 753                  $select = $select."$field = ?";
 754              } else {
 755                  $qs = str_repeat(',?', $count);
 756                  $qs = ltrim($qs, ',');
 757                  $select = $select."$field IN ($qs)";
 758              }
 759          }
 760          return array($select, $params);
 761      }
 762  
 763      /**
 764       * Constructs 'IN()' or '=' sql fragment
 765       * @param mixed $items A single value or array of values for the expression.
 766       * @param int $type Parameter bounding type : SQL_PARAMS_QM or SQL_PARAMS_NAMED.
 767       * @param string $prefix Named parameter placeholder prefix (a unique counter value is appended to each parameter name).
 768       * @param bool $equal True means we want to equate to the constructed expression, false means we don't want to equate to it.
 769       * @param mixed $onemptyitems This defines the behavior when the array of items provided is empty. Defaults to false,
 770       *              meaning throw exceptions. Other values will become part of the returned SQL fragment.
 771       * @throws coding_exception | dml_exception
 772       * @return array A list containing the constructed sql fragment and an array of parameters.
 773       */
 774      public function get_in_or_equal($items, $type=SQL_PARAMS_QM, $prefix='param', $equal=true, $onemptyitems=false) {
 775  
 776          // default behavior, throw exception on empty array
 777          if (is_array($items) and empty($items) and $onemptyitems === false) {
 778              throw new coding_exception('moodle_database::get_in_or_equal() does not accept empty arrays');
 779          }
 780          // handle $onemptyitems on empty array of items
 781          if (is_array($items) and empty($items)) {
 782              if (is_null($onemptyitems)) {             // Special case, NULL value
 783                  $sql = $equal ? ' IS NULL' : ' IS NOT NULL';
 784                  return (array($sql, array()));
 785              } else {
 786                  $items = array($onemptyitems);        // Rest of cases, prepare $items for std processing
 787              }
 788          }
 789  
 790          if ($type == SQL_PARAMS_QM) {
 791              if (!is_array($items) or count($items) == 1) {
 792                  $sql = $equal ? '= ?' : '<> ?';
 793                  $items = (array)$items;
 794                  $params = array_values($items);
 795              } else {
 796                  if ($equal) {
 797                      $sql = 'IN ('.implode(',', array_fill(0, count($items), '?')).')';
 798                  } else {
 799                      $sql = 'NOT IN ('.implode(',', array_fill(0, count($items), '?')).')';
 800                  }
 801                  $params = array_values($items);
 802              }
 803  
 804          } else if ($type == SQL_PARAMS_NAMED) {
 805              if (empty($prefix)) {
 806                  $prefix = 'param';
 807              }
 808  
 809              if (!is_array($items)){
 810                  $param = $prefix.$this->inorequaluniqueindex++;
 811                  $sql = $equal ? "= :$param" : "<> :$param";
 812                  $params = array($param=>$items);
 813              } else if (count($items) == 1) {
 814                  $param = $prefix.$this->inorequaluniqueindex++;
 815                  $sql = $equal ? "= :$param" : "<> :$param";
 816                  $item = reset($items);
 817                  $params = array($param=>$item);
 818              } else {
 819                  $params = array();
 820                  $sql = array();
 821                  foreach ($items as $item) {
 822                      $param = $prefix.$this->inorequaluniqueindex++;
 823                      $params[$param] = $item;
 824                      $sql[] = ':'.$param;
 825                  }
 826                  if ($equal) {
 827                      $sql = 'IN ('.implode(',', $sql).')';
 828                  } else {
 829                      $sql = 'NOT IN ('.implode(',', $sql).')';
 830                  }
 831              }
 832  
 833          } else {
 834              throw new dml_exception('typenotimplement');
 835          }
 836          return array($sql, $params);
 837      }
 838  
 839      /**
 840       * Converts short table name {tablename} to the real prefixed table name in given sql.
 841       * @param string $sql The sql to be operated on.
 842       * @return string The sql with tablenames being prefixed with $CFG->prefix
 843       */
 844      protected function fix_table_names($sql) {
 845          return preg_replace_callback(
 846              '/\{([a-z][a-z0-9_]*)\}/',
 847              function($matches) {
 848                  return $this->fix_table_name($matches[1]);
 849              },
 850              $sql
 851          );
 852      }
 853  
 854      /**
 855       * Adds the prefix to the table name.
 856       *
 857       * @param string $tablename The table name
 858       * @return string The prefixed table name
 859       */
 860      protected function fix_table_name($tablename) {
 861          return $this->prefix . $tablename;
 862      }
 863  
 864      /**
 865       * Internal private utitlity function used to fix parameters.
 866       * Used with {@link preg_replace_callback()}
 867       * @param array $match Refer to preg_replace_callback usage for description.
 868       * @return string
 869       */
 870      private function _fix_sql_params_dollar_callback($match) {
 871          $this->fix_sql_params_i++;
 872          return "\$".$this->fix_sql_params_i;
 873      }
 874  
 875      /**
 876       * Detects object parameters and throws exception if found
 877       * @param mixed $value
 878       * @return void
 879       * @throws coding_exception if object detected
 880       */
 881      protected function detect_objects($value) {
 882          if (is_object($value)) {
 883              throw new coding_exception('Invalid database query parameter value', 'Objects are are not allowed: '.get_class($value));
 884          }
 885      }
 886  
 887      /**
 888       * Normalizes sql query parameters and verifies parameters.
 889       * @param string $sql The query or part of it.
 890       * @param array $params The query parameters.
 891       * @return array (sql, params, type of params)
 892       */
 893      public function fix_sql_params($sql, array $params=null) {
 894          $params = (array)$params; // mke null array if needed
 895          $allowed_types = $this->allowed_param_types();
 896  
 897          // convert table names
 898          $sql = $this->fix_table_names($sql);
 899  
 900          // cast booleans to 1/0 int and detect forbidden objects
 901          foreach ($params as $key => $value) {
 902              $this->detect_objects($value);
 903              $params[$key] = is_bool($value) ? (int)$value : $value;
 904          }
 905  
 906          // NICOLAS C: Fixed regexp for negative backwards look-ahead of double colons. Thanks for Sam Marshall's help
 907          $named_count = preg_match_all('/(?<!:):[a-z][a-z0-9_]*/', $sql, $named_matches); // :: used in pgsql casts
 908          $dollar_count = preg_match_all('/\$[1-9][0-9]*/', $sql, $dollar_matches);
 909          $q_count     = substr_count($sql, '?');
 910  
 911          // Optionally add debug trace to sql as a comment.
 912          $sql = $this->add_sql_debugging($sql);
 913  
 914          $count = 0;
 915  
 916          if ($named_count) {
 917              $type = SQL_PARAMS_NAMED;
 918              $count = $named_count;
 919  
 920          }
 921          if ($dollar_count) {
 922              if ($count) {
 923                  throw new dml_exception('mixedtypesqlparam');
 924              }
 925              $type = SQL_PARAMS_DOLLAR;
 926              $count = $dollar_count;
 927  
 928          }
 929          if ($q_count) {
 930              if ($count) {
 931                  throw new dml_exception('mixedtypesqlparam');
 932              }
 933              $type = SQL_PARAMS_QM;
 934              $count = $q_count;
 935  
 936          }
 937  
 938          if (!$count) {
 939               // ignore params
 940              if ($allowed_types & SQL_PARAMS_NAMED) {
 941                  return array($sql, array(), SQL_PARAMS_NAMED);
 942              } else if ($allowed_types & SQL_PARAMS_QM) {
 943                  return array($sql, array(), SQL_PARAMS_QM);
 944              } else {
 945                  return array($sql, array(), SQL_PARAMS_DOLLAR);
 946              }
 947          }
 948  
 949          if ($count > count($params)) {
 950              $a = new stdClass;
 951              $a->expected = $count;
 952              $a->actual = count($params);
 953              throw new dml_exception('invalidqueryparam', $a);
 954          }
 955  
 956          $target_type = $allowed_types;
 957  
 958          if ($type & $allowed_types) { // bitwise AND
 959              if ($count == count($params)) {
 960                  if ($type == SQL_PARAMS_QM) {
 961                      return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based array required
 962                  } else {
 963                      //better do the validation of names below
 964                  }
 965              }
 966              // needs some fixing or validation - there might be more params than needed
 967              $target_type = $type;
 968          }
 969  
 970          if ($type == SQL_PARAMS_NAMED) {
 971              $finalparams = array();
 972              foreach ($named_matches[0] as $key) {
 973                  $key = trim($key, ':');
 974                  if (!array_key_exists($key, $params)) {
 975                      throw new dml_exception('missingkeyinsql', $key, '');
 976                  }
 977                  if (strlen($key) > 30) {
 978                      throw new coding_exception(
 979                              "Placeholder names must be 30 characters or shorter. '" .
 980                              $key . "' is too long.", $sql);
 981                  }
 982                  $finalparams[$key] = $params[$key];
 983              }
 984              if ($count != count($finalparams)) {
 985                  throw new dml_exception('duplicateparaminsql');
 986              }
 987  
 988              if ($target_type & SQL_PARAMS_QM) {
 989                  $sql = preg_replace('/(?<!:):[a-z][a-z0-9_]*/', '?', $sql);
 990                  return array($sql, array_values($finalparams), SQL_PARAMS_QM); // 0-based required
 991              } else if ($target_type & SQL_PARAMS_NAMED) {
 992                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
 993              } else {  // $type & SQL_PARAMS_DOLLAR
 994                  //lambda-style functions eat memory - we use globals instead :-(
 995                  $this->fix_sql_params_i = 0;
 996                  $sql = preg_replace_callback('/(?<!:):[a-z][a-z0-9_]*/', array($this, '_fix_sql_params_dollar_callback'), $sql);
 997                  return array($sql, array_values($finalparams), SQL_PARAMS_DOLLAR); // 0-based required
 998              }
 999  
1000          } else if ($type == SQL_PARAMS_DOLLAR) {
1001              if ($target_type & SQL_PARAMS_DOLLAR) {
1002                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
1003              } else if ($target_type & SQL_PARAMS_QM) {
1004                  $sql = preg_replace('/\$[0-9]+/', '?', $sql);
1005                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
1006              } else { //$target_type & SQL_PARAMS_NAMED
1007                  $sql = preg_replace('/\$([0-9]+)/', ':param\\1', $sql);
1008                  $finalparams = array();
1009                  foreach ($params as $key=>$param) {
1010                      $key++;
1011                      $finalparams['param'.$key] = $param;
1012                  }
1013                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
1014              }
1015  
1016          } else { // $type == SQL_PARAMS_QM
1017              if (count($params) != $count) {
1018                  $params = array_slice($params, 0, $count);
1019              }
1020  
1021              if ($target_type & SQL_PARAMS_QM) {
1022                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
1023              } else if ($target_type & SQL_PARAMS_NAMED) {
1024                  $finalparams = array();
1025                  $pname = 'param0';
1026                  $parts = explode('?', $sql);
1027                  $sql = array_shift($parts);
1028                  foreach ($parts as $part) {
1029                      $param = array_shift($params);
1030                      $pname++;
1031                      $sql .= ':'.$pname.$part;
1032                      $finalparams[$pname] = $param;
1033                  }
1034                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
1035              } else {  // $type & SQL_PARAMS_DOLLAR
1036                  //lambda-style functions eat memory - we use globals instead :-(
1037                  $this->fix_sql_params_i = 0;
1038                  $sql = preg_replace_callback('/\?/', array($this, '_fix_sql_params_dollar_callback'), $sql);
1039                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
1040              }
1041          }
1042      }
1043  
1044      /**
1045       * Add an SQL comment to trace all sql calls back to the calling php code
1046       * @param string $sql Original sql
1047       * @return string Instrumented sql
1048       */
1049      protected function add_sql_debugging(string $sql): string {
1050          global $CFG;
1051  
1052          if (!property_exists($CFG, 'debugsqltrace')) {
1053              return $sql;
1054          }
1055  
1056          $level = $CFG->debugsqltrace;
1057  
1058          if (empty($level)) {
1059              return $sql;
1060          }
1061  
1062          $callers = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
1063  
1064          // Ignore moodle_database internals.
1065          $callers = array_filter($callers, function($caller) {
1066              return empty($caller['class']) || $caller['class'] != 'moodle_database';
1067          });
1068  
1069          $callers = array_slice($callers, 0, $level);
1070  
1071          $text = trim(format_backtrace($callers, true));
1072  
1073          // Convert all linebreaks to SQL comments, optionally
1074          // also eating any * formatting.
1075          $text = preg_replace("/(^|\n)\*?\s*/", "\n-- ", $text);
1076  
1077          // Convert all ? to 'unknown' in the sql coment so these don't get
1078          // caught by fix_sql_params().
1079          $text = str_replace('?', 'unknown', $text);
1080  
1081          // Convert tokens like :test to ::test for the same reason.
1082          $text = preg_replace('/(?<!:):[a-z][a-z0-9_]*/', ':\0', $text);
1083  
1084          return $sql . $text;
1085      }
1086  
1087  
1088      /**
1089       * Ensures that limit params are numeric and positive integers, to be passed to the database.
1090       * We explicitly treat null, '' and -1 as 0 in order to provide compatibility with how limit
1091       * values have been passed historically.
1092       *
1093       * @param int $limitfrom Where to start results from
1094       * @param int $limitnum How many results to return
1095       * @return array Normalised limit params in array($limitfrom, $limitnum)
1096       */
1097      protected function normalise_limit_from_num($limitfrom, $limitnum) {
1098          global $CFG;
1099  
1100          // We explicilty treat these cases as 0.
1101          if ($limitfrom === null || $limitfrom === '' || $limitfrom === -1) {
1102              $limitfrom = 0;
1103          }
1104          if ($limitnum === null || $limitnum === '' || $limitnum === -1) {
1105              $limitnum = 0;
1106          }
1107  
1108          if ($CFG->debugdeveloper) {
1109              if (!is_numeric($limitfrom)) {
1110                  $strvalue = var_export($limitfrom, true);
1111                  debugging("Non-numeric limitfrom parameter detected: $strvalue, did you pass the correct arguments?",
1112                      DEBUG_DEVELOPER);
1113              } else if ($limitfrom < 0) {
1114                  debugging("Negative limitfrom parameter detected: $limitfrom, did you pass the correct arguments?",
1115                      DEBUG_DEVELOPER);
1116              }
1117  
1118              if (!is_numeric($limitnum)) {
1119                  $strvalue = var_export($limitnum, true);
1120                  debugging("Non-numeric limitnum parameter detected: $strvalue, did you pass the correct arguments?",
1121                      DEBUG_DEVELOPER);
1122              } else if ($limitnum < 0) {
1123                  debugging("Negative limitnum parameter detected: $limitnum, did you pass the correct arguments?",
1124                      DEBUG_DEVELOPER);
1125              }
1126          }
1127  
1128          $limitfrom = (int)$limitfrom;
1129          $limitnum  = (int)$limitnum;
1130          $limitfrom = max(0, $limitfrom);
1131          $limitnum  = max(0, $limitnum);
1132  
1133          return array($limitfrom, $limitnum);
1134      }
1135  
1136      /**
1137       * Return tables in database WITHOUT current prefix.
1138       * @param bool $usecache if true, returns list of cached tables.
1139       * @return array of table names in lowercase and without prefix
1140       */
1141      public abstract function get_tables($usecache=true);
1142  
1143      /**
1144       * Return table indexes - everything lowercased.
1145       * @param string $table The table we want to get indexes from.
1146       * @return array An associative array of indexes containing 'unique' flag and 'columns' being indexed
1147       */
1148      public abstract function get_indexes($table);
1149  
1150      /**
1151       * Returns detailed information about columns in table. This information is cached internally.
1152       *
1153       * @param string $table The table's name.
1154       * @param bool $usecache Flag to use internal cacheing. The default is true.
1155       * @return database_column_info[] of database_column_info objects indexed with column names
1156       */
1157      public function get_columns($table, $usecache = true): array {
1158          if (!$table) { // Table not specified, return empty array directly.
1159              return [];
1160          }
1161  
1162          if ($usecache) {
1163              if ($this->temptables->is_temptable($table)) {
1164                  if ($data = $this->get_temp_tables_cache()->get($table)) {
1165                      return $data;
1166                  }
1167              } else {
1168                  if ($data = $this->get_metacache()->get($table)) {
1169                      return $data;
1170                  }
1171              }
1172          }
1173  
1174          $structure = $this->fetch_columns($table);
1175  
1176          if ($usecache) {
1177              if ($this->temptables->is_temptable($table)) {
1178                  $this->get_temp_tables_cache()->set($table, $structure);
1179              } else {
1180                  $this->get_metacache()->set($table, $structure);
1181              }
1182          }
1183  
1184          return $structure;
1185      }
1186  
1187      /**
1188       * Returns detailed information about columns in table. This information is cached internally.
1189       *
1190       * @param string $table The table's name.
1191       * @return database_column_info[] of database_column_info objects indexed with column names
1192       */
1193      protected abstract function fetch_columns(string $table): array;
1194  
1195      /**
1196       * Normalise values based on varying RDBMS's dependencies (booleans, LOBs...)
1197       *
1198       * @param database_column_info $column column metadata corresponding with the value we are going to normalise
1199       * @param mixed $value value we are going to normalise
1200       * @return mixed the normalised value
1201       */
1202      protected abstract function normalise_value($column, $value);
1203  
1204      /**
1205       * Resets the internal column details cache
1206       *
1207       * @param array|null $tablenames an array of xmldb table names affected by this request.
1208       * @return void
1209       */
1210      public function reset_caches($tablenames = null) {
1211          if (!empty($tablenames)) {
1212              $dbmetapurged = false;
1213              foreach ($tablenames as $tablename) {
1214                  if ($this->temptables->is_temptable($tablename)) {
1215                      $this->get_temp_tables_cache()->delete($tablename);
1216                  } else if ($dbmetapurged === false) {
1217                      $this->tables = null;
1218                      $this->get_metacache()->purge();
1219                      $this->metacache = null;
1220                      $dbmetapurged = true;
1221                  }
1222              }
1223          } else {
1224              $this->get_temp_tables_cache()->purge();
1225              $this->tables = null;
1226              // Purge MUC as well.
1227              $this->get_metacache()->purge();
1228              $this->metacache = null;
1229          }
1230      }
1231  
1232      /**
1233       * Returns the sql generator used for db manipulation.
1234       * Used mostly in upgrade.php scripts.
1235       * @return database_manager The instance used to perform ddl operations.
1236       * @see lib/ddl/database_manager.php
1237       */
1238      public function get_manager() {
1239          global $CFG;
1240  
1241          if (!$this->database_manager) {
1242              require_once($CFG->libdir.'/ddllib.php');
1243  
1244              $classname = $this->get_dbfamily().'_sql_generator';
1245              require_once("$CFG->libdir/ddl/$classname.php");
1246              $generator = new $classname($this, $this->temptables);
1247  
1248              $this->database_manager = new database_manager($this, $generator);
1249          }
1250          return $this->database_manager;
1251      }
1252  
1253      /**
1254       * Attempts to change db encoding to UTF-8 encoding if possible.
1255       * @return bool True is successful.
1256       */
1257      public function change_db_encoding() {
1258          return false;
1259      }
1260  
1261      /**
1262       * Checks to see if the database is in unicode mode?
1263       * @return bool
1264       */
1265      public function setup_is_unicodedb() {
1266          return true;
1267      }
1268  
1269      /**
1270       * Enable/disable very detailed debugging.
1271       * @param bool $state
1272       * @return void
1273       */
1274      public function set_debug($state) {
1275          $this->debug = $state;
1276      }
1277  
1278      /**
1279       * Returns debug status
1280       * @return bool $state
1281       */
1282      public function get_debug() {
1283          return $this->debug;
1284      }
1285  
1286      /**
1287       * Enable/disable detailed sql logging
1288       *
1289       * @deprecated since Moodle 2.9
1290       */
1291      public function set_logging($state) {
1292          throw new coding_exception('set_logging() can not be used any more.');
1293      }
1294  
1295      /**
1296       * Do NOT use in code, this is for use by database_manager only!
1297       * @param string|array $sql query or array of queries
1298       * @param array|null $tablenames an array of xmldb table names affected by this request.
1299       * @return bool true
1300       * @throws ddl_change_structure_exception A DDL specific exception is thrown for any errors.
1301       */
1302      public abstract function change_database_structure($sql, $tablenames = null);
1303  
1304      /**
1305       * Executes a general sql query. Should be used only when no other method suitable.
1306       * Do NOT use this to make changes in db structure, use database_manager methods instead!
1307       * @param string $sql query
1308       * @param array $params query parameters
1309       * @return bool true
1310       * @throws dml_exception A DML specific exception is thrown for any errors.
1311       */
1312      public abstract function execute($sql, array $params=null);
1313  
1314      /**
1315       * Get a number of records as a moodle_recordset where all the given conditions met.
1316       *
1317       * Selects records from the table $table.
1318       *
1319       * If specified, only records meeting $conditions.
1320       *
1321       * If specified, the results will be sorted as specified by $sort. This
1322       * is added to the SQL as "ORDER BY $sort". Example values of $sort
1323       * might be "time ASC" or "time DESC".
1324       *
1325       * If $fields is specified, only those fields are returned.
1326       *
1327       * Since this method is a little less readable, use of it should be restricted to
1328       * code where it's possible there might be large datasets being returned.  For known
1329       * small datasets use get_records - it leads to simpler code.
1330       *
1331       * If you only want some of the records, specify $limitfrom and $limitnum.
1332       * The query will skip the first $limitfrom records (according to the sort
1333       * order) and then return the next $limitnum records. If either of $limitfrom
1334       * or $limitnum is specified, both must be present.
1335       *
1336       * The return value is a moodle_recordset
1337       * if the query succeeds. If an error occurs, false is returned.
1338       *
1339       * @param string $table the table to query.
1340       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1341       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1342       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1343       * @param int $limitfrom return a subset of records, starting at this point (optional).
1344       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1345       * @return moodle_recordset A moodle_recordset instance
1346       * @throws dml_exception A DML specific exception is thrown for any errors.
1347       */
1348      public function get_recordset($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1349          list($select, $params) = $this->where_clause($table, $conditions);
1350          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1351      }
1352  
1353      /**
1354       * Get a number of records as a moodle_recordset where one field match one list of values.
1355       *
1356       * Only records where $field takes one of the values $values are returned.
1357       * $values must be an array of values.
1358       *
1359       * Other arguments and the return type are like {@link function get_recordset}.
1360       *
1361       * @param string $table the table to query.
1362       * @param string $field a field to check (optional).
1363       * @param array $values array of values the field must have
1364       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1365       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1366       * @param int $limitfrom return a subset of records, starting at this point (optional).
1367       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1368       * @return moodle_recordset A moodle_recordset instance.
1369       * @throws dml_exception A DML specific exception is thrown for any errors.
1370       */
1371      public function get_recordset_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1372          list($select, $params) = $this->where_clause_list($field, $values);
1373          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1374      }
1375  
1376      /**
1377       * Get a number of records as a moodle_recordset which match a particular WHERE clause.
1378       *
1379       * If given, $select is used as the SELECT parameter in the SQL query,
1380       * otherwise all records from the table are returned.
1381       *
1382       * Other arguments and the return type are like {@link function get_recordset}.
1383       *
1384       * @param string $table the table to query.
1385       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1386       * @param array $params array of sql parameters
1387       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1388       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1389       * @param int $limitfrom return a subset of records, starting at this point (optional).
1390       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1391       * @return moodle_recordset A moodle_recordset instance.
1392       * @throws dml_exception A DML specific exception is thrown for any errors.
1393       */
1394      public function get_recordset_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1395          $sql = "SELECT $fields FROM {".$table."}";
1396          if ($select) {
1397              $sql .= " WHERE $select";
1398          }
1399          if ($sort) {
1400              $sql .= " ORDER BY $sort";
1401          }
1402          return $this->get_recordset_sql($sql, $params, $limitfrom, $limitnum);
1403      }
1404  
1405      /**
1406       * Get a number of records as a moodle_recordset using a SQL statement.
1407       *
1408       * Since this method is a little less readable, use of it should be restricted to
1409       * code where it's possible there might be large datasets being returned.  For known
1410       * small datasets use get_records_sql - it leads to simpler code.
1411       *
1412       * The return type is like {@link function get_recordset}.
1413       *
1414       * @param string $sql the SQL select query to execute.
1415       * @param array $params array of sql parameters
1416       * @param int $limitfrom return a subset of records, starting at this point (optional).
1417       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1418       * @return moodle_recordset A moodle_recordset instance.
1419       * @throws dml_exception A DML specific exception is thrown for any errors.
1420       */
1421      public abstract function get_recordset_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1422  
1423      /**
1424       * Get all records from a table.
1425       *
1426       * This method works around potential memory problems and may improve performance,
1427       * this method may block access to table until the recordset is closed.
1428       *
1429       * @param string $table Name of database table.
1430       * @return moodle_recordset A moodle_recordset instance {@link function get_recordset}.
1431       * @throws dml_exception A DML specific exception is thrown for any errors.
1432       */
1433      public function export_table_recordset($table) {
1434          return $this->get_recordset($table, array());
1435      }
1436  
1437      /**
1438       * Get a number of records as an array of objects where all the given conditions met.
1439       *
1440       * If the query succeeds and returns at least one record, the
1441       * return value is an array of objects, one object for each
1442       * record found. The array key is the value from the first
1443       * column of the result set. The object associated with that key
1444       * has a member variable for each column of the results.
1445       *
1446       * @param string $table the table to query.
1447       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1448       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1449       * @param string $fields a comma separated list of fields to return (optional, by default
1450       *   all fields are returned). The first field will be used as key for the
1451       *   array so must be a unique field such as 'id'.
1452       * @param int $limitfrom return a subset of records, starting at this point (optional).
1453       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1454       * @return array An array of Objects indexed by first column.
1455       * @throws dml_exception A DML specific exception is thrown for any errors.
1456       */
1457      public function get_records($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1458          list($select, $params) = $this->where_clause($table, $conditions);
1459          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1460      }
1461  
1462      /**
1463       * Get a number of records as an array of objects where one field match one list of values.
1464       *
1465       * Return value is like {@link function get_records}.
1466       *
1467       * @param string $table The database table to be checked against.
1468       * @param string $field The field to search
1469       * @param array $values An array of values
1470       * @param string $sort Sort order (as valid SQL sort parameter)
1471       * @param string $fields A comma separated list of fields to be returned from the chosen table. If specified,
1472       *   the first field should be a unique one such as 'id' since it will be used as a key in the associative
1473       *   array.
1474       * @param int $limitfrom return a subset of records, starting at this point (optional).
1475       * @param int $limitnum return a subset comprising this many records in total (optional).
1476       * @return array An array of objects indexed by first column
1477       * @throws dml_exception A DML specific exception is thrown for any errors.
1478       */
1479      public function get_records_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1480          list($select, $params) = $this->where_clause_list($field, $values);
1481          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1482      }
1483  
1484      /**
1485       * Get a number of records as an array of objects which match a particular WHERE clause.
1486       *
1487       * Return value is like {@link function get_records}.
1488       *
1489       * @param string $table The table to query.
1490       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1491       * @param array $params An array of sql parameters
1492       * @param string $sort An order to sort the results in (optional, a valid SQL ORDER BY parameter).
1493       * @param string $fields A comma separated list of fields to return
1494       *   (optional, by default all fields are returned). The first field will be used as key for the
1495       *   array so must be a unique field such as 'id'.
1496       * @param int $limitfrom return a subset of records, starting at this point (optional).
1497       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1498       * @return array of objects indexed by first column
1499       * @throws dml_exception A DML specific exception is thrown for any errors.
1500       */
1501      public function get_records_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1502          if ($select) {
1503              $select = "WHERE $select";
1504          }
1505          if ($sort) {
1506              $sort = " ORDER BY $sort";
1507          }
1508          return $this->get_records_sql("SELECT $fields FROM {" . $table . "} $select $sort", $params, $limitfrom, $limitnum);
1509      }
1510  
1511      /**
1512       * Get a number of records as an array of objects using a SQL statement.
1513       *
1514       * Return value is like {@link function get_records}.
1515       *
1516       * @param string $sql the SQL select query to execute. The first column of this SELECT statement
1517       *   must be a unique value (usually the 'id' field), as it will be used as the key of the
1518       *   returned array.
1519       * @param array $params array of sql parameters
1520       * @param int $limitfrom return a subset of records, starting at this point (optional).
1521       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1522       * @return array of objects indexed by first column
1523       * @throws dml_exception A DML specific exception is thrown for any errors.
1524       */
1525      public abstract function get_records_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1526  
1527      /**
1528       * Get the first two columns from a number of records as an associative array where all the given conditions met.
1529       *
1530       * Arguments are like {@link function get_recordset}.
1531       *
1532       * If no errors occur the return value
1533       * is an associative whose keys come from the first field of each record,
1534       * and whose values are the corresponding second fields.
1535       * False is returned if an error occurs.
1536       *
1537       * @param string $table the table to query.
1538       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1539       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1540       * @param string $fields a comma separated list of fields to return - the number of fields should be 2!
1541       * @param int $limitfrom return a subset of records, starting at this point (optional).
1542       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1543       * @return array an associative array
1544       * @throws dml_exception A DML specific exception is thrown for any errors.
1545       */
1546      public function get_records_menu($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1547          $menu = array();
1548          if ($records = $this->get_records($table, $conditions, $sort, $fields, $limitfrom, $limitnum)) {
1549              foreach ($records as $record) {
1550                  $record = (array)$record;
1551                  $key   = array_shift($record);
1552                  $value = array_shift($record);
1553                  $menu[$key] = $value;
1554              }
1555          }
1556          return $menu;
1557      }
1558  
1559      /**
1560       * Get the first two columns from a number of records as an associative array which match a particular WHERE clause.
1561       *
1562       * Arguments are like {@link function get_recordset_select}.
1563       * Return value is like {@link function get_records_menu}.
1564       *
1565       * @param string $table The database table to be checked against.
1566       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1567       * @param array $params array of sql parameters
1568       * @param string $sort Sort order (optional) - a valid SQL order parameter
1569       * @param string $fields A comma separated list of fields to be returned from the chosen table - the number of fields should be 2!
1570       * @param int $limitfrom return a subset of records, starting at this point (optional).
1571       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1572       * @return array an associative array
1573       * @throws dml_exception A DML specific exception is thrown for any errors.
1574       */
1575      public function get_records_select_menu($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1576          $menu = array();
1577          if ($records = $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum)) {
1578              foreach ($records as $record) {
1579                  $record = (array)$record;
1580                  $key   = array_shift($record);
1581                  $value = array_shift($record);
1582                  $menu[$key] = $value;
1583              }
1584          }
1585          return $menu;
1586      }
1587  
1588      /**
1589       * Get the first two columns from a number of records as an associative array using a SQL statement.
1590       *
1591       * Arguments are like {@link function get_recordset_sql}.
1592       * Return value is like {@link function get_records_menu}.
1593       *
1594       * @param string $sql The SQL string you wish to be executed.
1595       * @param array $params array of sql parameters
1596       * @param int $limitfrom return a subset of records, starting at this point (optional).
1597       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1598       * @return array an associative array
1599       * @throws dml_exception A DML specific exception is thrown for any errors.
1600       */
1601      public function get_records_sql_menu($sql, array $params=null, $limitfrom=0, $limitnum=0) {
1602          $menu = array();
1603          if ($records = $this->get_records_sql($sql, $params, $limitfrom, $limitnum)) {
1604              foreach ($records as $record) {
1605                  $record = (array)$record;
1606                  $key   = array_shift($record);
1607                  $value = array_shift($record);
1608                  $menu[$key] = $value;
1609              }
1610          }
1611          return $menu;
1612      }
1613  
1614      /**
1615       * Get a single database record as an object where all the given conditions met.
1616       *
1617       * @param string $table The table to select from.
1618       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1619       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1620       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1621       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1622       *                        MUST_EXIST means we will throw an exception if no record or multiple records found.
1623       *
1624       * @todo MDL-30407 MUST_EXIST option should not throw a dml_exception, it should throw a different exception as it's a requested check.
1625       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1626       * @throws dml_exception A DML specific exception is thrown for any errors.
1627       */
1628      public function get_record($table, array $conditions, $fields='*', $strictness=IGNORE_MISSING) {
1629          list($select, $params) = $this->where_clause($table, $conditions);
1630          return $this->get_record_select($table, $select, $params, $fields, $strictness);
1631      }
1632  
1633      /**
1634       * Get a single database record as an object which match a particular WHERE clause.
1635       *
1636       * @param string $table The database table to be checked against.
1637       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1638       * @param array $params array of sql parameters
1639       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1640       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1641       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1642       *                        MUST_EXIST means throw exception if no record or multiple records found
1643       * @return stdClass|false a fieldset object containing the first matching record, false or exception if error not found depending on mode
1644       * @throws dml_exception A DML specific exception is thrown for any errors.
1645       */
1646      public function get_record_select($table, $select, array $params=null, $fields='*', $strictness=IGNORE_MISSING) {
1647          if ($select) {
1648              $select = "WHERE $select";
1649          }
1650          try {
1651              return $this->get_record_sql("SELECT $fields FROM {" . $table . "} $select", $params, $strictness);
1652          } catch (dml_missing_record_exception $e) {
1653              // create new exception which will contain correct table name
1654              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1655          }
1656      }
1657  
1658      /**
1659       * Get a single database record as an object using a SQL statement.
1660       *
1661       * The SQL statement should normally only return one record.
1662       * It is recommended to use get_records_sql() if more matches possible!
1663       *
1664       * @param string $sql The SQL string you wish to be executed, should normally only return one record.
1665       * @param array $params array of sql parameters
1666       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1667       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1668       *                        MUST_EXIST means throw exception if no record or multiple records found
1669       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1670       * @throws dml_exception A DML specific exception is thrown for any errors.
1671       */
1672      public function get_record_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1673          $strictness = (int)$strictness; // we support true/false for BC reasons too
1674          if ($strictness == IGNORE_MULTIPLE) {
1675              $count = 1;
1676          } else {
1677              $count = 0;
1678          }
1679          if (!$records = $this->get_records_sql($sql, $params, 0, $count)) {
1680              // not found
1681              if ($strictness == MUST_EXIST) {
1682                  throw new dml_missing_record_exception('', $sql, $params);
1683              }
1684              return false;
1685          }
1686  
1687          if (count($records) > 1) {
1688              if ($strictness == MUST_EXIST) {
1689                  throw new dml_multiple_records_exception($sql, $params);
1690              }
1691              debugging('Error: mdb->get_record() found more than one record!');
1692          }
1693  
1694          $return = reset($records);
1695          return $return;
1696      }
1697  
1698      /**
1699       * Get a single field value from a table record where all the given conditions met.
1700       *
1701       * @param string $table the table to query.
1702       * @param string $return the field to return the value of.
1703       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1704       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1705       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1706       *                        MUST_EXIST means throw exception if no record or multiple records found
1707       * @return mixed the specified value false if not found
1708       * @throws dml_exception A DML specific exception is thrown for any errors.
1709       */
1710      public function get_field($table, $return, array $conditions, $strictness=IGNORE_MISSING) {
1711          list($select, $params) = $this->where_clause($table, $conditions);
1712          return $this->get_field_select($table, $return, $select, $params, $strictness);
1713      }
1714  
1715      /**
1716       * Get a single field value from a table record which match a particular WHERE clause.
1717       *
1718       * @param string $table the table to query.
1719       * @param string $return the field to return the value of.
1720       * @param string $select A fragment of SQL to be used in a where clause returning one row with one column
1721       * @param array $params array of sql parameters
1722       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1723       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1724       *                        MUST_EXIST means throw exception if no record or multiple records found
1725       * @return mixed the specified value false if not found
1726       * @throws dml_exception A DML specific exception is thrown for any errors.
1727       */
1728      public function get_field_select($table, $return, $select, array $params=null, $strictness=IGNORE_MISSING) {
1729          if ($select) {
1730              $select = "WHERE $select";
1731          }
1732          try {
1733              return $this->get_field_sql("SELECT $return FROM {" . $table . "} $select", $params, $strictness);
1734          } catch (dml_missing_record_exception $e) {
1735              // create new exception which will contain correct table name
1736              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1737          }
1738      }
1739  
1740      /**
1741       * Get a single field value (first field) using a SQL statement.
1742       *
1743       * @param string $sql The SQL query returning one row with one column
1744       * @param array $params array of sql parameters
1745       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1746       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1747       *                        MUST_EXIST means throw exception if no record or multiple records found
1748       * @return mixed the specified value false if not found
1749       * @throws dml_exception A DML specific exception is thrown for any errors.
1750       */
1751      public function get_field_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1752          if (!$record = $this->get_record_sql($sql, $params, $strictness)) {
1753              return false;
1754          }
1755  
1756          $record = (array)$record;
1757          return reset($record); // first column
1758      }
1759  
1760      /**
1761       * Selects records and return values of chosen field as an array which match a particular WHERE clause.
1762       *
1763       * @param string $table the table to query.
1764       * @param string $return the field we are intered in
1765       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1766       * @param array $params array of sql parameters
1767       * @return array of values
1768       * @throws dml_exception A DML specific exception is thrown for any errors.
1769       */
1770      public function get_fieldset_select($table, $return, $select, array $params=null) {
1771          if ($select) {
1772              $select = "WHERE $select";
1773          }
1774          return $this->get_fieldset_sql("SELECT $return FROM {" . $table . "} $select", $params);
1775      }
1776  
1777      /**
1778       * Selects records and return values (first field) as an array using a SQL statement.
1779       *
1780       * @param string $sql The SQL query
1781       * @param array $params array of sql parameters
1782       * @return array of values
1783       * @throws dml_exception A DML specific exception is thrown for any errors.
1784       */
1785      public abstract function get_fieldset_sql($sql, array $params=null);
1786  
1787      /**
1788       * Insert new record into database, as fast as possible, no safety checks, lobs not supported.
1789       * @param string $table name
1790       * @param mixed $params data record as object or array
1791       * @param bool $returnid Returns id of inserted record.
1792       * @param bool $bulk true means repeated inserts expected
1793       * @param bool $customsequence true if 'id' included in $params, disables $returnid
1794       * @return bool|int true or new id
1795       * @throws dml_exception A DML specific exception is thrown for any errors.
1796       */
1797      public abstract function insert_record_raw($table, $params, $returnid=true, $bulk=false, $customsequence=false);
1798  
1799      /**
1800       * Insert a record into a table and return the "id" field if required.
1801       *
1802       * Some conversions and safety checks are carried out. Lobs are supported.
1803       * If the return ID isn't required, then this just reports success as true/false.
1804       * $data is an object containing needed data
1805       * @param string $table The database table to be inserted into
1806       * @param object|array $dataobject A data object with values for one or more fields in the record
1807       * @param bool $returnid Should the id of the newly created record entry be returned? If this option is not requested then true/false is returned.
1808       * @param bool $bulk Set to true is multiple inserts are expected
1809       * @return bool|int true or new id
1810       * @throws dml_exception A DML specific exception is thrown for any errors.
1811       */
1812      public abstract function insert_record($table, $dataobject, $returnid=true, $bulk=false);
1813  
1814      /**
1815       * Insert multiple records into database as fast as possible.
1816       *
1817       * Order of inserts is maintained, but the operation is not atomic,
1818       * use transactions if necessary.
1819       *
1820       * This method is intended for inserting of large number of small objects,
1821       * do not use for huge objects with text or binary fields.
1822       *
1823       * @since Moodle 2.7
1824       *
1825       * @param string $table  The database table to be inserted into
1826       * @param array|Traversable $dataobjects list of objects to be inserted, must be compatible with foreach
1827       * @return void does not return new record ids
1828       *
1829       * @throws coding_exception if data objects have different structure
1830       * @throws dml_exception A DML specific exception is thrown for any errors.
1831       */
1832      public function insert_records($table, $dataobjects) {
1833          if (!is_array($dataobjects) and !($dataobjects instanceof Traversable)) {
1834              throw new coding_exception('insert_records() passed non-traversable object');
1835          }
1836  
1837          $fields = null;
1838          // Note: override in driver if there is a faster way.
1839          foreach ($dataobjects as $dataobject) {
1840              if (!is_array($dataobject) and !is_object($dataobject)) {
1841                  throw new coding_exception('insert_records() passed invalid record object');
1842              }
1843              $dataobject = (array)$dataobject;
1844              if ($fields === null) {
1845                  $fields = array_keys($dataobject);
1846              } else if ($fields !== array_keys($dataobject)) {
1847                  throw new coding_exception('All dataobjects in insert_records() must have the same structure!');
1848              }
1849              $this->insert_record($table, $dataobject, false);
1850          }
1851      }
1852  
1853      /**
1854       * Import a record into a table, id field is required.
1855       * Safety checks are NOT carried out. Lobs are supported.
1856       *
1857       * @param string $table name of database table to be inserted into
1858       * @param object $dataobject A data object with values for one or more fields in the record
1859       * @return bool true
1860       * @throws dml_exception A DML specific exception is thrown for any errors.
1861       */
1862      public abstract function import_record($table, $dataobject);
1863  
1864      /**
1865       * Update record in database, as fast as possible, no safety checks, lobs not supported.
1866       * @param string $table name
1867       * @param mixed $params data record as object or array
1868       * @param bool $bulk True means repeated updates expected.
1869       * @return bool true
1870       * @throws dml_exception A DML specific exception is thrown for any errors.
1871       */
1872      public abstract function update_record_raw($table, $params, $bulk=false);
1873  
1874      /**
1875       * Update a record in a table
1876       *
1877       * $dataobject is an object containing needed data
1878       * Relies on $dataobject having a variable "id" to
1879       * specify the record to update
1880       *
1881       * @param string $table The database table to be checked against.
1882       * @param object $dataobject An object with contents equal to fieldname=>fieldvalue. Must have an entry for 'id' to map to the table specified.
1883       * @param bool $bulk True means repeated updates expected.
1884       * @return bool true
1885       * @throws dml_exception A DML specific exception is thrown for any errors.
1886       */
1887      public abstract function update_record($table, $dataobject, $bulk=false);
1888  
1889      /**
1890       * Set a single field in every table record where all the given conditions met.
1891       *
1892       * @param string $table The database table to be checked against.
1893       * @param string $newfield the field to set.
1894       * @param string $newvalue the value to set the field to.
1895       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1896       * @return bool true
1897       * @throws dml_exception A DML specific exception is thrown for any errors.
1898       */
1899      public function set_field($table, $newfield, $newvalue, array $conditions=null) {
1900          list($select, $params) = $this->where_clause($table, $conditions);
1901          return $this->set_field_select($table, $newfield, $newvalue, $select, $params);
1902      }
1903  
1904      /**
1905       * Set a single field in every table record which match a particular WHERE clause.
1906       *
1907       * @param string $table The database table to be checked against.
1908       * @param string $newfield the field to set.
1909       * @param string $newvalue the value to set the field to.
1910       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1911       * @param array $params array of sql parameters
1912       * @return bool true
1913       * @throws dml_exception A DML specific exception is thrown for any errors.
1914       */
1915      public abstract function set_field_select($table, $newfield, $newvalue, $select, array $params=null);
1916  
1917  
1918      /**
1919       * Count the records in a table where all the given conditions met.
1920       *
1921       * @param string $table The table to query.
1922       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1923       * @return int The count of records returned from the specified criteria.
1924       * @throws dml_exception A DML specific exception is thrown for any errors.
1925       */
1926      public function count_records($table, array $conditions=null) {
1927          list($select, $params) = $this->where_clause($table, $conditions);
1928          return $this->count_records_select($table, $select, $params);
1929      }
1930  
1931      /**
1932       * Count the records in a table which match a particular WHERE clause.
1933       *
1934       * @param string $table The database table to be checked against.
1935       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1936       * @param array $params array of sql parameters
1937       * @param string $countitem The count string to be used in the SQL call. Default is COUNT('x').
1938       * @return int The count of records returned from the specified criteria.
1939       * @throws dml_exception A DML specific exception is thrown for any errors.
1940       */
1941      public function count_records_select($table, $select, array $params=null, $countitem="COUNT('x')") {
1942          if ($select) {
1943              $select = "WHERE $select";
1944          }
1945          return $this->count_records_sql("SELECT $countitem FROM {" . $table . "} $select", $params);
1946      }
1947  
1948      /**
1949       * Get the result of a SQL SELECT COUNT(...) query.
1950       *
1951       * Given a query that counts rows, return that count. (In fact,
1952       * given any query, return the first field of the first record
1953       * returned. However, this method should only be used for the
1954       * intended purpose.) If an error occurs, 0 is returned.
1955       *
1956       * @param string $sql The SQL string you wish to be executed.
1957       * @param array $params array of sql parameters
1958       * @return int the count
1959       * @throws dml_exception A DML specific exception is thrown for any errors.
1960       */
1961      public function count_records_sql($sql, array $params=null) {
1962          $count = $this->get_field_sql($sql, $params);
1963          if ($count === false or !is_number($count) or $count < 0) {
1964              throw new coding_exception("count_records_sql() expects the first field to contain non-negative number from COUNT(), '$count' found instead.");
1965          }
1966          return (int)$count;
1967      }
1968  
1969      /**
1970       * Test whether a record exists in a table where all the given conditions met.
1971       *
1972       * @param string $table The table to check.
1973       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1974       * @return bool true if a matching record exists, else false.
1975       * @throws dml_exception A DML specific exception is thrown for any errors.
1976       */
1977      public function record_exists($table, array $conditions) {
1978          list($select, $params) = $this->where_clause($table, $conditions);
1979          return $this->record_exists_select($table, $select, $params);
1980      }
1981  
1982      /**
1983       * Test whether any records exists in a table which match a particular WHERE clause.
1984       *
1985       * @param string $table The database table to be checked against.
1986       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1987       * @param array $params array of sql parameters
1988       * @return bool true if a matching record exists, else false.
1989       * @throws dml_exception A DML specific exception is thrown for any errors.
1990       */
1991      public function record_exists_select($table, $select, array $params=null) {
1992          if ($select) {
1993              $select = "WHERE $select";
1994          }
1995          return $this->record_exists_sql("SELECT 'x' FROM {" . $table . "} $select", $params);
1996      }
1997  
1998      /**
1999       * Test whether a SQL SELECT statement returns any records.
2000       *
2001       * This function returns true if the SQL statement executes
2002       * without any errors and returns at least one record.
2003       *
2004       * @param string $sql The SQL statement to execute.
2005       * @param array $params array of sql parameters
2006       * @return bool true if the SQL executes without errors and returns at least one record.
2007       * @throws dml_exception A DML specific exception is thrown for any errors.
2008       */
2009      public function record_exists_sql($sql, array $params=null) {
2010          $mrs = $this->get_recordset_sql($sql, $params, 0, 1);
2011          $return = $mrs->valid();
2012          $mrs->close();
2013          return $return;
2014      }
2015  
2016      /**
2017       * Delete the records from a table where all the given conditions met.
2018       * If conditions not specified, table is truncated.
2019       *
2020       * @param string $table the table to delete from.
2021       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
2022       * @return bool true.
2023       * @throws dml_exception A DML specific exception is thrown for any errors.
2024       */
2025      public function delete_records($table, array $conditions=null) {
2026          // truncate is drop/create (DDL), not transactional safe,
2027          // so we don't use the shortcut within them. MDL-29198
2028          if (is_null($conditions) && empty($this->transactions)) {
2029              return $this->execute("TRUNCATE TABLE {".$table."}");
2030          }
2031          list($select, $params) = $this->where_clause($table, $conditions);
2032          return $this->delete_records_select($table, $select, $params);
2033      }
2034  
2035      /**
2036       * Delete the records from a table where one field match one list of values.
2037       *
2038       * @param string $table the table to delete from.
2039       * @param string $field The field to search
2040       * @param array $values array of values
2041       * @return bool true.
2042       * @throws dml_exception A DML specific exception is thrown for any errors.
2043       */
2044      public function delete_records_list($table, $field, array $values) {
2045          list($select, $params) = $this->where_clause_list($field, $values);
2046          return $this->delete_records_select($table, $select, $params);
2047      }
2048  
2049      /**
2050       * Deletes records from a table using a subquery. The subquery should return a list of values
2051       * in a single column, which match one field from the table being deleted.
2052       *
2053       * The $alias parameter must be set to the name of the single column in your subquery result
2054       * (e.g. if the subquery is 'SELECT id FROM whatever', then it should be 'id'). This is not
2055       * needed on most databases, but MySQL requires it.
2056       *
2057       * (On database where the subquery is inefficient, it is implemented differently.)
2058       *
2059       * @param string $table Table to delete from
2060       * @param string $field Field in table to match
2061       * @param string $alias Name of single column in subquery e.g. 'id'
2062       * @param string $subquery Subquery that will return values of the field to delete
2063       * @param array $params Parameters for subquery
2064       * @throws dml_exception If there is any error
2065       * @since Moodle 3.10
2066       */
2067      public function delete_records_subquery(string $table, string $field, string $alias,
2068              string $subquery, array $params = []): void {
2069          $this->delete_records_select($table, $field . ' IN (' . $subquery . ')', $params);
2070      }
2071  
2072      /**
2073       * Delete one or more records from a table which match a particular WHERE clause.
2074       *
2075       * @param string $table The database table to be checked against.
2076       * @param string $select A fragment of SQL to be used in a where clause in the SQL call (used to define the selection criteria).
2077       * @param array $params array of sql parameters
2078       * @return bool true.
2079       * @throws dml_exception A DML specific exception is thrown for any errors.
2080       */
2081      public abstract function delete_records_select($table, $select, array $params=null);
2082  
2083      /**
2084       * Returns the FROM clause required by some DBs in all SELECT statements.
2085       *
2086       * To be used in queries not having FROM clause to provide cross_db
2087       * Most DBs don't need it, hence the default is ''
2088       * @return string
2089       */
2090      public function sql_null_from_clause() {
2091          return '';
2092      }
2093  
2094      /**
2095       * Returns the SQL text to be used in order to perform one bitwise AND operation
2096       * between 2 integers.
2097       *
2098       * NOTE: The SQL result is a number and can not be used directly in
2099       *       SQL condition, please compare it to some number to get a bool!!
2100       *
2101       * @param int $int1 First integer in the operation.
2102       * @param int $int2 Second integer in the operation.
2103       * @return string The piece of SQL code to be used in your statement.
2104       */
2105      public function sql_bitand($int1, $int2) {
2106          return '((' . $int1 . ') & (' . $int2 . '))';
2107      }
2108  
2109      /**
2110       * Returns the SQL text to be used in order to perform one bitwise NOT operation
2111       * with 1 integer.
2112       *
2113       * @param int $int1 The operand integer in the operation.
2114       * @return string The piece of SQL code to be used in your statement.
2115       */
2116      public function sql_bitnot($int1) {
2117          return '(~(' . $int1 . '))';
2118      }
2119  
2120      /**
2121       * Returns the SQL text to be used in order to perform one bitwise OR operation
2122       * between 2 integers.
2123       *
2124       * NOTE: The SQL result is a number and can not be used directly in
2125       *       SQL condition, please compare it to some number to get a bool!!
2126       *
2127       * @param int $int1 The first operand integer in the operation.
2128       * @param int $int2 The second operand integer in the operation.
2129       * @return string The piece of SQL code to be used in your statement.
2130       */
2131      public function sql_bitor($int1, $int2) {
2132          return '((' . $int1 . ') | (' . $int2 . '))';
2133      }
2134  
2135      /**
2136       * Returns the SQL text to be used in order to perform one bitwise XOR operation
2137       * between 2 integers.
2138       *
2139       * NOTE: The SQL result is a number and can not be used directly in
2140       *       SQL condition, please compare it to some number to get a bool!!
2141       *
2142       * @param int $int1 The first operand integer in the operation.
2143       * @param int $int2 The second operand integer in the operation.
2144       * @return string The piece of SQL code to be used in your statement.
2145       */
2146      public function sql_bitxor($int1, $int2) {
2147          return '((' . $int1 . ') ^ (' . $int2 . '))';
2148      }
2149  
2150      /**
2151       * Returns the SQL text to be used in order to perform module '%'
2152       * operation - remainder after division
2153       *
2154       * @param int $int1 The first operand integer in the operation.
2155       * @param int $int2 The second operand integer in the operation.
2156       * @return string The piece of SQL code to be used in your statement.
2157       */
2158      public function sql_modulo($int1, $int2) {
2159          return '((' . $int1 . ') % (' . $int2 . '))';
2160      }
2161  
2162      /**
2163       * Returns the cross db correct CEIL (ceiling) expression applied to fieldname.
2164       * note: Most DBs use CEIL(), hence it's the default here.
2165       *
2166       * @param string $fieldname The field (or expression) we are going to ceil.
2167       * @return string The piece of SQL code to be used in your ceiling statement.
2168       */
2169      public function sql_ceil($fieldname) {
2170          return ' CEIL(' . $fieldname . ')';
2171      }
2172  
2173      /**
2174       * Return SQL for casting to char of given field/expression. Default implementation performs implicit cast using
2175       * concatenation with an empty string
2176       *
2177       * @param string $field Table field or SQL expression to be cast
2178       * @return string
2179       */
2180      public function sql_cast_to_char(string $field): string {
2181          return $this->sql_concat("''", $field);
2182      }
2183  
2184      /**
2185       * Returns the SQL to be used in order to CAST one CHAR column to INTEGER.
2186       *
2187       * Be aware that the CHAR column you're trying to cast contains really
2188       * int values or the RDBMS will throw an error!
2189       *
2190       * @param string $fieldname The name of the field to be casted.
2191       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2192       * @return string The piece of SQL code to be used in your statement.
2193       */
2194      public function sql_cast_char2int($fieldname, $text=false) {
2195          return ' ' . $fieldname . ' ';
2196      }
2197  
2198      /**
2199       * Returns the SQL to be used in order to CAST one CHAR column to REAL number.
2200       *
2201       * Be aware that the CHAR column you're trying to cast contains really
2202       * numbers or the RDBMS will throw an error!
2203       *
2204       * @param string $fieldname The name of the field to be casted.
2205       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2206       * @return string The piece of SQL code to be used in your statement.
2207       */
2208      public function sql_cast_char2real($fieldname, $text=false) {
2209          return ' ' . $fieldname . ' ';
2210      }
2211  
2212      /**
2213       * Returns the SQL to be used in order to an UNSIGNED INTEGER column to SIGNED.
2214       *
2215       * (Only MySQL needs this. MySQL things that 1 * -1 = 18446744073709551615
2216       * if the 1 comes from an unsigned column).
2217       *
2218       * @deprecated since 2.3
2219       * @param string $fieldname The name of the field to be cast
2220       * @return string The piece of SQL code to be used in your statement.
2221       */
2222      public function sql_cast_2signed($fieldname) {
2223          return ' ' . $fieldname . ' ';
2224      }
2225  
2226      /**
2227       * Returns the SQL text to be used to compare one TEXT (clob) column with
2228       * one varchar column, because some RDBMS doesn't support such direct
2229       * comparisons.
2230       *
2231       * @param string $fieldname The name of the TEXT field we need to order by
2232       * @param int $numchars Number of chars to use for the ordering (defaults to 32).
2233       * @return string The piece of SQL code to be used in your statement.
2234       */
2235      public function sql_compare_text($fieldname, $numchars=32) {
2236          return $this->sql_order_by_text($fieldname, $numchars);
2237      }
2238  
2239      /**
2240       * Returns an equal (=) or not equal (<>) part of a query.
2241       *
2242       * Note the use of this method may lead to slower queries (full scans) so
2243       * use it only when needed and against already reduced data sets.
2244       *
2245       * @since Moodle 3.2
2246       *
2247       * @param string $fieldname Usually the name of the table column.
2248       * @param string $param Usually the bound query parameter (?, :named).
2249       * @param bool $casesensitive Use case sensitive search when set to true (default).
2250       * @param bool $accentsensitive Use accent sensitive search when set to true (default). (not all databases support accent insensitive)
2251       * @param bool $notequal True means not equal (<>)
2252       * @return string The SQL code fragment.
2253       */
2254      public function sql_equal($fieldname, $param, $casesensitive = true, $accentsensitive = true, $notequal = false) {
2255          // Note that, by default, it's assumed that the correct sql equal operations are
2256          // case sensitive. Only databases not observing this behavior must override the method.
2257          // Also, accent sensitiveness only will be handled by databases supporting it.
2258          $equalop = $notequal ? '<>' : '=';
2259          if ($casesensitive) {
2260              return "$fieldname $equalop $param";
2261          } else {
2262              return "LOWER($fieldname) $equalop LOWER($param)";
2263          }
2264      }
2265  
2266      /**
2267       * Returns 'LIKE' part of a query.
2268       *
2269       * @param string $fieldname Usually the name of the table column.
2270       * @param string $param Usually the bound query parameter (?, :named).
2271       * @param bool $casesensitive Use case sensitive search when set to true (default).
2272       * @param bool $accentsensitive Use accent sensitive search when set to true (default). (not all databases support accent insensitive)
2273       * @param bool $notlike True means "NOT LIKE".
2274       * @param string $escapechar The escape char for '%' and '_'.
2275       * @return string The SQL code fragment.
2276       */
2277      public function sql_like($fieldname, $param, $casesensitive = true, $accentsensitive = true, $notlike = false, $escapechar = '\\') {
2278          if (strpos($param, '%') !== false) {
2279              debugging('Potential SQL injection detected, sql_like() expects bound parameters (? or :named)');
2280          }
2281          $LIKE = $notlike ? 'NOT LIKE' : 'LIKE';
2282          // by default ignore any sensitiveness - each database does it in a different way
2283          return "$fieldname $LIKE $param ESCAPE '$escapechar'";
2284      }
2285  
2286      /**
2287       * Escape sql LIKE special characters like '_' or '%'.
2288       * @param string $text The string containing characters needing escaping.
2289       * @param string $escapechar The desired escape character, defaults to '\\'.
2290       * @return string The escaped sql LIKE string.
2291       */
2292      public function sql_like_escape($text, $escapechar = '\\') {
2293          $text = str_replace('_', $escapechar.'_', $text);
2294          $text = str_replace('%', $escapechar.'%', $text);
2295          return $text;
2296      }
2297  
2298      /**
2299       * Returns the proper SQL to do CONCAT between the elements(fieldnames) passed.
2300       *
2301       * This function accepts variable number of string parameters.
2302       * All strings/fieldnames will used in the SQL concatenate statement generated.
2303       *
2304       * @return string The SQL to concatenate strings passed in.
2305       * @uses func_get_args()  and thus parameters are unlimited OPTIONAL number of additional field names.
2306       */
2307      public abstract function sql_concat();
2308  
2309      /**
2310       * Returns the proper SQL to do CONCAT between the elements passed
2311       * with a given separator
2312       *
2313       * @param string $separator The separator desired for the SQL concatenating $elements.
2314       * @param array  $elements The array of strings to be concatenated.
2315       * @return string The SQL to concatenate the strings.
2316       */
2317      public abstract function sql_concat_join($separator="' '", $elements=array());
2318  
2319      /**
2320       * Return SQL for performing group concatenation on given field/expression
2321       *
2322       * @param string $field Table field or SQL expression to be concatenated
2323       * @param string $separator The separator desired between each concatetated field
2324       * @param string $sort Ordering of the concatenated field
2325       * @return string
2326       */
2327      public abstract function sql_group_concat(string $field, string $separator = ', ', string $sort = ''): string;
2328  
2329      /**
2330       * Returns the proper SQL (for the dbms in use) to concatenate $firstname and $lastname
2331       *
2332       * @todo MDL-31233 This may not be needed here.
2333       *
2334       * @param string $first User's first name (default:'firstname').
2335       * @param string $last User's last name (default:'lastname').
2336       * @return string The SQL to concatenate strings.
2337       */
2338      function sql_fullname($first='firstname', $last='lastname') {
2339          return $this->sql_concat($first, "' '", $last);
2340      }
2341  
2342      /**
2343       * Returns the SQL text to be used to order by one TEXT (clob) column, because
2344       * some RDBMS doesn't support direct ordering of such fields.
2345       *
2346       * Note that the use or queries being ordered by TEXT columns must be minimised,
2347       * because it's really slooooooow.
2348       *
2349       * @param string $fieldname The name of the TEXT field we need to order by.
2350       * @param int $numchars The number of chars to use for the ordering (defaults to 32).
2351       * @return string The piece of SQL code to be used in your statement.
2352       */
2353      public function sql_order_by_text($fieldname, $numchars=32) {
2354          return $fieldname;
2355      }
2356  
2357      /**
2358       * Returns the SQL text to be used to order by columns, standardising the return
2359       * pattern of null values across database types to sort nulls first when ascending
2360       * and last when descending.
2361       *
2362       * @param string $fieldname The name of the field we need to sort by.
2363       * @param int $sort An order to sort the results in.
2364       * @return string The piece of SQL code to be used in your statement.
2365       */
2366      public function sql_order_by_null(string $fieldname, int $sort = SORT_ASC): string {
2367          return $fieldname . ' ' . ($sort == SORT_ASC ? 'ASC' : 'DESC');
2368      }
2369  
2370      /**
2371       * Returns the SQL text to be used to calculate the length in characters of one expression.
2372       * @param string $fieldname The fieldname/expression to calculate its length in characters.
2373       * @return string the piece of SQL code to be used in the statement.
2374       */
2375      public function sql_length($fieldname) {
2376          return ' LENGTH(' . $fieldname . ')';
2377      }
2378  
2379      /**
2380       * Returns the proper substr() SQL text used to extract substrings from DB
2381       * NOTE: this was originally returning only function name
2382       *
2383       * @param string $expr Some string field, no aggregates.
2384       * @param mixed $start Integer or expression evaluating to integer (1 based value; first char has index 1)
2385       * @param mixed $length Optional integer or expression evaluating to integer.
2386       * @return string The sql substring extraction fragment.
2387       */
2388      public function sql_substr($expr, $start, $length=false) {
2389          if (count(func_get_args()) < 2) {
2390              throw new coding_exception('moodle_database::sql_substr() requires at least two parameters', 'Originally this function was only returning name of SQL substring function, it now requires all parameters.');
2391          }
2392          if ($length === false) {
2393              return "SUBSTR($expr, $start)";
2394          } else {
2395              return "SUBSTR($expr, $start, $length)";
2396          }
2397      }
2398  
2399      /**
2400       * Returns the SQL for returning searching one string for the location of another.
2401       *
2402       * Note, there is no guarantee which order $needle, $haystack will be in
2403       * the resulting SQL so when using this method, and both arguments contain
2404       * placeholders, you should use named placeholders.
2405       *
2406       * @param string $needle the SQL expression that will be searched for.
2407       * @param string $haystack the SQL expression that will be searched in.
2408       * @return string The required searching SQL part.
2409       */
2410      public function sql_position($needle, $haystack) {
2411          // Implementation using standard SQL.
2412          return "POSITION(($needle) IN ($haystack))";
2413      }
2414  
2415      /**
2416       * This used to return empty string replacement character.
2417       *
2418       * @deprecated use bound parameter with empty string instead
2419       *
2420       * @return string An empty string.
2421       */
2422      function sql_empty() {
2423          debugging("sql_empty() is deprecated, please use empty string '' as sql parameter value instead", DEBUG_DEVELOPER);
2424          return '';
2425      }
2426  
2427      /**
2428       * Returns the proper SQL to know if one field is empty.
2429       *
2430       * Note that the function behavior strongly relies on the
2431       * parameters passed describing the field so, please,  be accurate
2432       * when specifying them.
2433       *
2434       * Also, note that this function is not suitable to look for
2435       * fields having NULL contents at all. It's all for empty values!
2436       *
2437       * This function should be applied in all the places where conditions of
2438       * the type:
2439       *
2440       *     ... AND fieldname = '';
2441       *
2442       * are being used. Final result for text fields should be:
2443       *
2444       *     ... AND ' . sql_isempty('tablename', 'fieldname', true/false, true);
2445       *
2446       * and for varchar fields result should be:
2447       *
2448       *    ... AND fieldname = :empty; "; $params['empty'] = '';
2449       *
2450       * (see parameters description below)
2451       *
2452       * @param string $tablename Name of the table (without prefix). Not used for now but can be
2453       *                          necessary in the future if we want to use some introspection using
2454       *                          meta information against the DB. /// TODO ///
2455       * @param string $fieldname Name of the field we are going to check
2456       * @param bool $nullablefield For specifying if the field is nullable (true) or no (false) in the DB.
2457       * @param bool $textfield For specifying if it is a text (also called clob) field (true) or a varchar one (false)
2458       * @return string the sql code to be added to check for empty values
2459       */
2460      public function sql_isempty($tablename, $fieldname, $nullablefield, $textfield) {
2461          return " ($fieldname = '') ";
2462      }
2463  
2464      /**
2465       * Returns the proper SQL to know if one field is not empty.
2466       *
2467       * Note that the function behavior strongly relies on the
2468       * parameters passed describing the field so, please,  be accurate
2469       * when specifying them.
2470       *
2471       * This function should be applied in all the places where conditions of
2472       * the type:
2473       *
2474       *     ... AND fieldname != '';
2475       *
2476       * are being used. Final result for text fields should be:
2477       *
2478       *     ... AND ' . sql_isnotempty('tablename', 'fieldname', true/false, true/false);
2479       *
2480       * and for varchar fields result should be:
2481       *
2482       *    ... AND fieldname != :empty; "; $params['empty'] = '';
2483       *
2484       * (see parameters description below)
2485       *
2486       * @param string $tablename Name of the table (without prefix). This is not used for now but can be
2487       *                          necessary in the future if we want to use some introspection using
2488       *                          meta information against the DB.
2489       * @param string $fieldname The name of the field we are going to check.
2490       * @param bool $nullablefield Specifies if the field is nullable (true) or not (false) in the DB.
2491       * @param bool $textfield Specifies if it is a text (also called clob) field (true) or a varchar one (false).
2492       * @return string The sql code to be added to check for non empty values.
2493       */
2494      public function sql_isnotempty($tablename, $fieldname, $nullablefield, $textfield) {
2495          return ' ( NOT ' . $this->sql_isempty($tablename, $fieldname, $nullablefield, $textfield) . ') ';
2496      }
2497  
2498      /**
2499       * Returns true if this database driver supports regex syntax when searching.
2500       * @return bool True if supported.
2501       */
2502      public function sql_regex_supported() {
2503          return false;
2504      }
2505  
2506      /**
2507       * Returns the driver specific syntax (SQL part) for matching regex positively or negatively (inverted matching).
2508       * Eg: 'REGEXP':'NOT REGEXP' or '~*' : '!~*'
2509       *
2510       * @param bool $positivematch
2511       * @param bool $casesensitive
2512       * @return string or empty if not supported
2513       */
2514      public function sql_regex($positivematch = true, $casesensitive = false) {
2515          return '';
2516      }
2517  
2518      /**
2519       * Returns the word-beginning boundary marker if this database driver supports regex syntax when searching.
2520       * @return string The word-beginning boundary marker. Otherwise, an empty string.
2521       */
2522      public function sql_regex_get_word_beginning_boundary_marker() {
2523          if ($this->sql_regex_supported()) {
2524              return '[[:<:]]';
2525          }
2526  
2527          return '';
2528      }
2529  
2530      /**
2531       * Returns the word-end boundary marker if this database driver supports regex syntax when searching.
2532       * @return string The word-end boundary marker. Otherwise, an empty string.
2533       */
2534      public function sql_regex_get_word_end_boundary_marker() {
2535          if ($this->sql_regex_supported()) {
2536              return '[[:>:]]';
2537          }
2538  
2539          return '';
2540      }
2541  
2542      /**
2543       * Returns the SQL that allows to find intersection of two or more queries
2544       *
2545       * @since Moodle 2.8
2546       *
2547       * @param array $selects array of SQL select queries, each of them only returns fields with the names from $fields
2548       * @param string $fields comma-separated list of fields (used only by some DB engines)
2549       * @return string SQL query that will return only values that are present in each of selects
2550       */
2551      public function sql_intersect($selects, $fields) {
2552          if (!count($selects)) {
2553              throw new coding_exception('sql_intersect() requires at least one element in $selects');
2554          } else if (count($selects) == 1) {
2555              return $selects[0];
2556          }
2557          static $aliascnt = 0;
2558          $rv = '('.$selects[0].')';
2559          for ($i = 1; $i < count($selects); $i++) {
2560              $rv .= " INTERSECT (".$selects[$i].')';
2561          }
2562          return $rv;
2563      }
2564  
2565      /**
2566       * Does this driver support tool_replace?
2567       *
2568       * @since Moodle 2.6.1
2569       * @return bool
2570       */
2571      public function replace_all_text_supported() {
2572          return false;
2573      }
2574  
2575      /**
2576       * Replace given text in all rows of column.
2577       *
2578       * @since Moodle 2.6.1
2579       * @param string $table name of the table
2580       * @param database_column_info $column
2581       * @param string $search
2582       * @param string $replace
2583       */
2584      public function replace_all_text($table, database_column_info $column, $search, $replace) {
2585          if (!$this->replace_all_text_supported()) {
2586              return;
2587          }
2588  
2589          // NOTE: override this methods if following standard compliant SQL
2590          //       does not work for your driver.
2591  
2592          // Enclose the column name by the proper quotes if it's a reserved word.
2593          $columnname = $this->get_manager()->generator->getEncQuoted($column->name);
2594  
2595          $searchsql = $this->sql_like($columnname, '?');
2596          $searchparam = '%'.$this->sql_like_escape($search).'%';
2597  
2598          $sql = "UPDATE {".$table."}
2599                         SET $columnname = REPLACE($columnname, ?, ?)
2600                       WHERE $searchsql";
2601  
2602          if ($column->meta_type === 'X') {
2603              $this->execute($sql, array($search, $replace, $searchparam));
2604  
2605          } else if ($column->meta_type === 'C') {
2606              if (core_text::strlen($search) < core_text::strlen($replace)) {
2607                  $colsize = $column->max_length;
2608                  $sql = "UPDATE {".$table."}
2609                         SET $columnname = " . $this->sql_substr("REPLACE(" . $columnname . ", ?, ?)", 1, $colsize) . "
2610                       WHERE $searchsql";
2611              }
2612              $this->execute($sql, array($search, $replace, $searchparam));
2613          }
2614      }
2615  
2616      /**
2617       * Analyze the data in temporary tables to force statistics collection after bulk data loads.
2618       *
2619       * @return void
2620       */
2621      public function update_temp_table_stats() {
2622          $this->temptables->update_stats();
2623      }
2624  
2625      /**
2626       * Checks and returns true if transactions are supported.
2627       *
2628       * It is not responsible to run productions servers
2629       * on databases without transaction support ;-)
2630       *
2631       * Override in driver if needed.
2632       *
2633       * @return bool
2634       */
2635      protected function transactions_supported() {
2636          // protected for now, this might be changed to public if really necessary
2637          return true;
2638      }
2639  
2640      /**
2641       * Returns true if a transaction is in progress.
2642       * @return bool
2643       */
2644      public function is_transaction_started() {
2645          return !empty($this->transactions);
2646      }
2647  
2648      /**
2649       * This is a test that throws an exception if transaction in progress.
2650       * This test does not force rollback of active transactions.
2651       * @return void
2652       * @throws dml_transaction_exception if stansaction active
2653       */
2654      public function transactions_forbidden() {
2655          if ($this->is_transaction_started()) {
2656              throw new dml_transaction_exception('This code can not be excecuted in transaction');
2657          }
2658      }
2659  
2660      /**
2661       * On DBs that support it, switch to transaction mode and begin a transaction
2662       * you'll need to ensure you call allow_commit() on the returned object
2663       * or your changes *will* be lost.
2664       *
2665       * this is _very_ useful for massive updates
2666       *
2667       * Delegated database transactions can be nested, but only one actual database
2668       * transaction is used for the outer-most delegated transaction. This method
2669       * returns a transaction object which you should keep until the end of the
2670       * delegated transaction. The actual database transaction will
2671       * only be committed if all the nested delegated transactions commit
2672       * successfully. If any part of the transaction rolls back then the whole
2673       * thing is rolled back.
2674       *
2675       * @return moodle_transaction
2676       */
2677      public function start_delegated_transaction() {
2678          $transaction = new moodle_transaction($this);
2679          $this->transactions[] = $transaction;
2680          if (count($this->transactions) == 1) {
2681              $this->begin_transaction();
2682          }
2683          return $transaction;
2684      }
2685  
2686      /**
2687       * Driver specific start of real database transaction,
2688       * this can not be used directly in code.
2689       * @return void
2690       */
2691      protected abstract function begin_transaction();
2692  
2693      /**
2694       * Indicates delegated transaction finished successfully.
2695       * The real database transaction is committed only if
2696       * all delegated transactions committed.
2697       * @param moodle_transaction $transaction The transaction to commit
2698       * @return void
2699       * @throws dml_transaction_exception Creates and throws transaction related exceptions.
2700       */
2701      public function commit_delegated_transaction(moodle_transaction $transaction) {
2702          if ($transaction->is_disposed()) {
2703              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2704          }
2705          // mark as disposed so that it can not be used again
2706          $transaction->dispose();
2707  
2708          if (empty($this->transactions)) {
2709              throw new dml_transaction_exception('Transaction not started', $transaction);
2710          }
2711  
2712          if ($this->force_rollback) {
2713              throw new dml_transaction_exception('Tried to commit transaction after lower level rollback', $transaction);
2714          }
2715  
2716          if ($transaction !== $this->transactions[count($this->transactions) - 1]) {
2717              // one incorrect commit at any level rollbacks everything
2718              $this->force_rollback = true;
2719              throw new dml_transaction_exception('Invalid transaction commit attempt', $transaction);
2720          }
2721  
2722          if (count($this->transactions) == 1) {
2723              // only commit the top most level
2724              $this->commit_transaction();
2725          }
2726          array_pop($this->transactions);
2727  
2728          if (empty($this->transactions)) {
2729              \core\event\manager::database_transaction_commited();
2730              \core\message\manager::database_transaction_commited();
2731          }
2732      }
2733  
2734      /**
2735       * Driver specific commit of real database transaction,
2736       * this can not be used directly in code.
2737       * @return void
2738       */
2739      protected abstract function commit_transaction();
2740  
2741      /**
2742       * Call when delegated transaction failed, this rolls back
2743       * all delegated transactions up to the top most level.
2744       *
2745       * In many cases you do not need to call this method manually,
2746       * because all open delegated transactions are rolled back
2747       * automatically if exceptions not caught.
2748       *
2749       * @param moodle_transaction $transaction An instance of a moodle_transaction.
2750       * @param Exception|Throwable $e The related exception/throwable to this transaction rollback.
2751       * @return void This does not return, instead the exception passed in will be rethrown.
2752       */
2753      public function rollback_delegated_transaction(moodle_transaction $transaction, $e) {
2754          if (!($e instanceof Exception) && !($e instanceof Throwable)) {
2755              // PHP7 - we catch Throwables in phpunit but can't use that as the type hint in PHP5.
2756              $e = new \coding_exception("Must be given an Exception or Throwable object!");
2757          }
2758          if ($transaction->is_disposed()) {
2759              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2760          }
2761          // mark as disposed so that it can not be used again
2762          $transaction->dispose();
2763  
2764          // one rollback at any level rollbacks everything
2765          $this->force_rollback = true;
2766  
2767          if (empty($this->transactions) or $transaction !== $this->transactions[count($this->transactions) - 1]) {
2768              // this may or may not be a coding problem, better just rethrow the exception,
2769              // because we do not want to loose the original $e
2770              throw $e;
2771          }
2772  
2773          if (count($this->transactions) == 1) {
2774              // only rollback the top most level
2775              $this->rollback_transaction();
2776          }
2777          array_pop($this->transactions);
2778          if (empty($this->transactions)) {
2779              // finally top most level rolled back
2780              $this->force_rollback = false;
2781              \core\event\manager::database_transaction_rolledback();
2782              \core\message\manager::database_transaction_rolledback();
2783          }
2784          throw $e;
2785      }
2786  
2787      /**
2788       * Driver specific abort of real database transaction,
2789       * this can not be used directly in code.
2790       * @return void
2791       */
2792      protected abstract function rollback_transaction();
2793  
2794      /**
2795       * Force rollback of all delegated transaction.
2796       * Does not throw any exceptions and does not log anything.
2797       *
2798       * This method should be used only from default exception handlers and other
2799       * core code.
2800       *
2801       * @return void
2802       */
2803      public function force_transaction_rollback() {
2804          if ($this->transactions) {
2805              try {
2806                  $this->rollback_transaction();
2807              } catch (dml_exception $e) {
2808                  // ignore any sql errors here, the connection might be broken
2809              }
2810          }
2811  
2812          // now enable transactions again
2813          $this->transactions = array();
2814          $this->force_rollback = false;
2815  
2816          \core\event\manager::database_transaction_rolledback();
2817          \core\message\manager::database_transaction_rolledback();
2818      }
2819  
2820      /**
2821       * Is session lock supported in this driver?
2822       * @return bool
2823       */
2824      public function session_lock_supported() {
2825          return false;
2826      }
2827  
2828      /**
2829       * Obtains the session lock.
2830       * @param int $rowid The id of the row with session record.
2831       * @param int $timeout The maximum allowed time to wait for the lock in seconds.
2832       * @return void
2833       * @throws dml_exception A DML specific exception is thrown for any errors.
2834       */
2835      public function get_session_lock($rowid, $timeout) {
2836          $this->used_for_db_sessions = true;
2837      }
2838  
2839      /**
2840       * Releases the session lock.
2841       * @param int $rowid The id of the row with session record.
2842       * @return void
2843       * @throws dml_exception A DML specific exception is thrown for any errors.
2844       */
2845      public function release_session_lock($rowid) {
2846      }
2847  
2848      /**
2849       * Returns the number of reads done by this database.
2850       * @return int Number of reads.
2851       */
2852      public function perf_get_reads() {
2853          return $this->reads;
2854      }
2855  
2856      /**
2857       * Returns whether we want to connect to slave database for read queries.
2858       * @return bool Want read only connection
2859       */
2860      public function want_read_slave(): bool {
2861          return false;
2862      }
2863  
2864      /**
2865       * Returns the number of reads before first write done by this database.
2866       * @return int Number of reads.
2867       */
2868      public function perf_get_reads_slave(): int {
2869          return 0;
2870      }
2871  
2872      /**
2873       * Returns the number of writes done by this database.
2874       * @return int Number of writes.
2875       */
2876      public function perf_get_writes() {
2877          return $this->writes;
2878      }
2879  
2880      /**
2881       * Returns the number of queries done by this database.
2882       * @return int Number of queries.
2883       */
2884      public function perf_get_queries() {
2885          return $this->writes + $this->reads;
2886      }
2887  
2888      /**
2889       * Time waiting for the database engine to finish running all queries.
2890       * @return float Number of seconds with microseconds
2891       */
2892      public function perf_get_queries_time() {
2893          return $this->queriestime;
2894      }
2895  
2896      /**
2897       * Whether the database is able to support full-text search or not.
2898       *
2899       * @return bool
2900       */
2901      public function is_fulltext_search_supported() {
2902          // No support unless specified.
2903          return false;
2904      }
2905  }