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   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  /**
  56   * Abstract class representing moodle database interface.
  57   * @link http://docs.moodle.org/dev/DML_functions
  58   *
  59   * @package    core_dml
  60   * @copyright  2008 Petr Skoda (http://skodak.org)
  61   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  62   */
  63  abstract class moodle_database {
  64  
  65      /** @var database_manager db manager which allows db structure modifications. */
  66      protected $database_manager;
  67      /** @var moodle_temptables temptables manager to provide cross-db support for temp tables. */
  68      protected $temptables;
  69      /** @var array Cache of table info. */
  70      protected $tables  = null;
  71  
  72      // db connection options
  73      /** @var string db host name. */
  74      protected $dbhost;
  75      /** @var string db host user. */
  76      protected $dbuser;
  77      /** @var string db host password. */
  78      protected $dbpass;
  79      /** @var string db name. */
  80      protected $dbname;
  81      /** @var string Prefix added to table names. */
  82      protected $prefix;
  83  
  84      /** @var array Database or driver specific options, such as sockets or TCP/IP db connections. */
  85      protected $dboptions;
  86  
  87      /** @var bool True means non-moodle external database used.*/
  88      protected $external;
  89  
  90      /** @var int The database reads (performance counter).*/
  91      protected $reads = 0;
  92      /** @var int The database writes (performance counter).*/
  93      protected $writes = 0;
  94      /** @var float Time queries took to finish, seconds with microseconds.*/
  95      protected $queriestime = 0;
  96  
  97      /** @var int Debug level. */
  98      protected $debug  = 0;
  99  
 100      /** @var string Last used query sql. */
 101      protected $last_sql;
 102      /** @var array Last query parameters. */
 103      protected $last_params;
 104      /** @var int Last query type. */
 105      protected $last_type;
 106      /** @var string Last extra info. */
 107      protected $last_extrainfo;
 108      /** @var float Last time in seconds with millisecond precision. */
 109      protected $last_time;
 110      /** @var bool Flag indicating logging of query in progress. This helps prevent infinite loops. */
 111      private $loggingquery = false;
 112  
 113      /** @var bool True if the db is used for db sessions. */
 114      protected $used_for_db_sessions = false;
 115  
 116      /** @var array Array containing open transactions. */
 117      private $transactions = array();
 118      /** @var bool Flag used to force rollback of all current transactions. */
 119      private $force_rollback = false;
 120  
 121      /** @var string MD5 of settings used for connection. Used by MUC as an identifier. */
 122      private $settingshash;
 123  
 124      /** @var cache_application for column info */
 125      protected $metacache;
 126  
 127      /** @var bool flag marking database instance as disposed */
 128      protected $disposed;
 129  
 130      /**
 131       * @var int internal temporary variable used to fix params. Its used by {@link _fix_sql_params_dollar_callback()}.
 132       */
 133      private $fix_sql_params_i;
 134      /**
 135       * @var int internal temporary variable used to guarantee unique parameters in each request. Its used by {@link get_in_or_equal()}.
 136       */
 137      private $inorequaluniqueindex = 1;
 138  
 139      /**
 140       * Constructor - Instantiates the database, specifying if it's external (connect to other systems) or not (Moodle DB).
 141       *              Note that this affects the decision of whether prefix checks must be performed or not.
 142       * @param bool $external True means that an external database is used.
 143       */
 144      public function __construct($external=false) {
 145          $this->external  = $external;
 146      }
 147  
 148      /**
 149       * Destructor - cleans up and flushes everything needed.
 150       */
 151      public function __destruct() {
 152          $this->dispose();
 153      }
 154  
 155      /**
 156       * Detects if all needed PHP stuff are installed for DB connectivity.
 157       * Note: can be used before connect()
 158       * @return mixed True if requirements are met, otherwise a string if something isn't installed.
 159       */
 160      public abstract function driver_installed();
 161  
 162      /**
 163       * Returns database table prefix
 164       * Note: can be used before connect()
 165       * @return string The prefix used in the database.
 166       */
 167      public function get_prefix() {
 168          return $this->prefix;
 169      }
 170  
 171      /**
 172       * Loads and returns a database instance with the specified type and library.
 173       *
 174       * The loaded class is within lib/dml directory and of the form: $type.'_'.$library.'_moodle_database'
 175       *
 176       * @param string $type Database driver's type. (eg: mysqli, pgsql, mssql, sqldrv, oci, etc.)
 177       * @param string $library Database driver's library (native, pdo, etc.)
 178       * @param bool $external True if this is an external database.
 179       * @return moodle_database driver object or null if error, for example of driver object see {@link mysqli_native_moodle_database}
 180       */
 181      public static function get_driver_instance($type, $library, $external = false) {
 182          global $CFG;
 183  
 184          $classname = $type.'_'.$library.'_moodle_database';
 185          $libfile   = "$CFG->libdir/dml/$classname.php";
 186  
 187          if (!file_exists($libfile)) {
 188              return null;
 189          }
 190  
 191          require_once($libfile);
 192          return new $classname($external);
 193      }
 194  
 195      /**
 196       * Returns the database vendor.
 197       * Note: can be used before connect()
 198       * @return string The db vendor name, usually the same as db family name.
 199       */
 200      public function get_dbvendor() {
 201          return $this->get_dbfamily();
 202      }
 203  
 204      /**
 205       * Returns the database family type. (This sort of describes the SQL 'dialect')
 206       * Note: can be used before connect()
 207       * @return string The db family name (mysql, postgres, mssql, oracle, etc.)
 208       */
 209      public abstract function get_dbfamily();
 210  
 211      /**
 212       * Returns a more specific database driver type
 213       * Note: can be used before connect()
 214       * @return string The db type mysqli, pgsql, oci, mssql, sqlsrv
 215       */
 216      protected abstract function get_dbtype();
 217  
 218      /**
 219       * Returns the general database library name
 220       * Note: can be used before connect()
 221       * @return string The db library type -  pdo, native etc.
 222       */
 223      protected abstract function get_dblibrary();
 224  
 225      /**
 226       * Returns the localised database type name
 227       * Note: can be used before connect()
 228       * @return string
 229       */
 230      public abstract function get_name();
 231  
 232      /**
 233       * Returns the localised database configuration help.
 234       * Note: can be used before connect()
 235       * @return string
 236       */
 237      public abstract function get_configuration_help();
 238  
 239      /**
 240       * Returns the localised database description
 241       * Note: can be used before connect()
 242       * @deprecated since 2.6
 243       * @return string
 244       */
 245      public function get_configuration_hints() {
 246          debugging('$DB->get_configuration_hints() method is deprecated, use $DB->get_configuration_help() instead');
 247          return $this->get_configuration_help();
 248      }
 249  
 250      /**
 251       * Returns the db related part of config.php
 252       * @return stdClass
 253       */
 254      public function export_dbconfig() {
 255          $cfg = new stdClass();
 256          $cfg->dbtype    = $this->get_dbtype();
 257          $cfg->dblibrary = $this->get_dblibrary();
 258          $cfg->dbhost    = $this->dbhost;
 259          $cfg->dbname    = $this->dbname;
 260          $cfg->dbuser    = $this->dbuser;
 261          $cfg->dbpass    = $this->dbpass;
 262          $cfg->prefix    = $this->prefix;
 263          if ($this->dboptions) {
 264              $cfg->dboptions = $this->dboptions;
 265          }
 266  
 267          return $cfg;
 268      }
 269  
 270      /**
 271       * Diagnose database and tables, this function is used
 272       * to verify database and driver settings, db engine types, etc.
 273       *
 274       * @return string null means everything ok, string means problem found.
 275       */
 276      public function diagnose() {
 277          return null;
 278      }
 279  
 280      /**
 281       * Connects to the database.
 282       * Must be called before other methods.
 283       * @param string $dbhost The database host.
 284       * @param string $dbuser The database user to connect as.
 285       * @param string $dbpass The password to use when connecting to the database.
 286       * @param string $dbname The name of the database being connected to.
 287       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 288       * @param array $dboptions driver specific options
 289       * @return bool true
 290       * @throws dml_connection_exception if error
 291       */
 292      public abstract function connect($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null);
 293  
 294      /**
 295       * Store various database settings
 296       * @param string $dbhost The database host.
 297       * @param string $dbuser The database user to connect as.
 298       * @param string $dbpass The password to use when connecting to the database.
 299       * @param string $dbname The name of the database being connected to.
 300       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 301       * @param array $dboptions driver specific options
 302       * @return void
 303       */
 304      protected function store_settings($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null) {
 305          $this->dbhost    = $dbhost;
 306          $this->dbuser    = $dbuser;
 307          $this->dbpass    = $dbpass;
 308          $this->dbname    = $dbname;
 309          $this->prefix    = $prefix;
 310          $this->dboptions = (array)$dboptions;
 311      }
 312  
 313      /**
 314       * Returns a hash for the settings used during connection.
 315       *
 316       * If not already requested it is generated and stored in a private property.
 317       *
 318       * @return string
 319       */
 320      protected function get_settings_hash() {
 321          if (empty($this->settingshash)) {
 322              $this->settingshash = md5($this->dbhost . $this->dbuser . $this->dbname . $this->prefix);
 323          }
 324          return $this->settingshash;
 325      }
 326  
 327      /**
 328       * Handle the creation and caching of the databasemeta information for all databases.
 329       *
 330       * TODO MDL-53267 impelement caching of cache::make() results when it's safe to do so.
 331       *
 332       * @return cache_application The databasemeta cachestore to complete operations on.
 333       */
 334      protected function get_metacache() {
 335          $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 336          return cache::make('core', 'databasemeta', $properties);
 337      }
 338  
 339      /**
 340       * Handle the creation and caching of the temporary tables.
 341       *
 342       * @return cache_application The temp_tables cachestore to complete operations on.
 343       */
 344      protected function get_temp_tables_cache() {
 345          // Using connection data to prevent collisions when using the same temp table name with different db connections.
 346          $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 347          return cache::make('core', 'temp_tables', $properties);
 348      }
 349  
 350      /**
 351       * Attempt to create the database
 352       * @param string $dbhost The database host.
 353       * @param string $dbuser The database user to connect as.
 354       * @param string $dbpass The password to use when connecting to the database.
 355       * @param string $dbname The name of the database being connected to.
 356       * @param array $dboptions An array of optional database options (eg: dbport)
 357       *
 358       * @return bool success True for successful connection. False otherwise.
 359       */
 360      public function create_database($dbhost, $dbuser, $dbpass, $dbname, array $dboptions=null) {
 361          return false;
 362      }
 363  
 364      /**
 365       * Returns transaction trace for debugging purposes.
 366       * @private to be used by core only
 367       * @return array or null if not in transaction.
 368       */
 369      public function get_transaction_start_backtrace() {
 370          if (!$this->transactions) {
 371              return null;
 372          }
 373          $lowesttransaction = end($this->transactions);
 374          return $lowesttransaction->get_backtrace();
 375      }
 376  
 377      /**
 378       * Closes the database connection and releases all resources
 379       * and memory (especially circular memory references).
 380       * Do NOT use connect() again, create a new instance if needed.
 381       * @return void
 382       */
 383      public function dispose() {
 384          if ($this->disposed) {
 385              return;
 386          }
 387          $this->disposed = true;
 388          if ($this->transactions) {
 389              $this->force_transaction_rollback();
 390          }
 391  
 392          if ($this->temptables) {
 393              $this->temptables->dispose();
 394              $this->temptables = null;
 395          }
 396          if ($this->database_manager) {
 397              $this->database_manager->dispose();
 398              $this->database_manager = null;
 399          }
 400          $this->tables  = null;
 401      }
 402  
 403      /**
 404       * This should be called before each db query.
 405       * @param string $sql The query string.
 406       * @param array $params An array of parameters.
 407       * @param int $type The type of query. ( SQL_QUERY_SELECT | SQL_QUERY_AUX | SQL_QUERY_INSERT | SQL_QUERY_UPDATE | SQL_QUERY_STRUCTURE )
 408       * @param mixed $extrainfo This is here for any driver specific extra information.
 409       * @return void
 410       */
 411      protected function query_start($sql, array $params=null, $type, $extrainfo=null) {
 412          if ($this->loggingquery) {
 413              return;
 414          }
 415          $this->last_sql       = $sql;
 416          $this->last_params    = $params;
 417          $this->last_type      = $type;
 418          $this->last_extrainfo = $extrainfo;
 419          $this->last_time      = microtime(true);
 420  
 421          switch ($type) {
 422              case SQL_QUERY_SELECT:
 423              case SQL_QUERY_AUX:
 424                  $this->reads++;
 425                  break;
 426              case SQL_QUERY_INSERT:
 427              case SQL_QUERY_UPDATE:
 428              case SQL_QUERY_STRUCTURE:
 429                  $this->writes++;
 430              default:
 431                  if ((PHPUNIT_TEST) || (defined('BEHAT_TEST') && BEHAT_TEST) ||
 432                      defined('BEHAT_SITE_RUNNING')) {
 433  
 434                      // Set list of tables that are updated.
 435                      require_once (__DIR__.'/../testing/classes/util.php');
 436                      testing_util::set_table_modified_by_sql($sql);
 437                  }
 438          }
 439  
 440          $this->print_debug($sql, $params);
 441      }
 442  
 443      /**
 444       * This should be called immediately after each db query. It does a clean up of resources.
 445       * It also throws exceptions if the sql that ran produced errors.
 446       * @param mixed $result The db specific result obtained from running a query.
 447       * @throws dml_read_exception | dml_write_exception | ddl_change_structure_exception
 448       * @return void
 449       */
 450      protected function query_end($result) {
 451          if ($this->loggingquery) {
 452              return;
 453          }
 454          if ($result !== false) {
 455              $this->query_log();
 456              // free memory
 457              $this->last_sql    = null;
 458              $this->last_params = null;
 459              $this->print_debug_time();
 460              return;
 461          }
 462  
 463          // remember current info, log queries may alter it
 464          $type   = $this->last_type;
 465          $sql    = $this->last_sql;
 466          $params = $this->last_params;
 467          $error  = $this->get_last_error();
 468  
 469          $this->query_log($error);
 470  
 471          switch ($type) {
 472              case SQL_QUERY_SELECT:
 473              case SQL_QUERY_AUX:
 474                  throw new dml_read_exception($error, $sql, $params);
 475              case SQL_QUERY_INSERT:
 476              case SQL_QUERY_UPDATE:
 477                  throw new dml_write_exception($error, $sql, $params);
 478              case SQL_QUERY_STRUCTURE:
 479                  $this->get_manager(); // includes ddl exceptions classes ;-)
 480                  throw new ddl_change_structure_exception($error, $sql);
 481          }
 482      }
 483  
 484      /**
 485       * This logs the last query based on 'logall', 'logslow' and 'logerrors' options configured via $CFG->dboptions .
 486       * @param string|bool $error or false if not error
 487       * @return void
 488       */
 489      public function query_log($error=false) {
 490          $logall    = !empty($this->dboptions['logall']);
 491          $logslow   = !empty($this->dboptions['logslow']) ? $this->dboptions['logslow'] : false;
 492          $logerrors = !empty($this->dboptions['logerrors']);
 493          $iserror   = ($error !== false);
 494  
 495          $time = $this->query_time();
 496  
 497          // Will be shown or not depending on MDL_PERF values rather than in dboptions['log*].
 498          $this->queriestime = $this->queriestime + $time;
 499  
 500          if ($logall or ($logslow and ($logslow < ($time+0.00001))) or ($iserror and $logerrors)) {
 501              $this->loggingquery = true;
 502              try {
 503                  $backtrace = debug_backtrace();
 504                  if ($backtrace) {
 505                      //remove query_log()
 506                      array_shift($backtrace);
 507                  }
 508                  if ($backtrace) {
 509                      //remove query_end()
 510                      array_shift($backtrace);
 511                  }
 512                  $log = new stdClass();
 513                  $log->qtype      = $this->last_type;
 514                  $log->sqltext    = $this->last_sql;
 515                  $log->sqlparams  = var_export((array)$this->last_params, true);
 516                  $log->error      = (int)$iserror;
 517                  $log->info       = $iserror ? $error : null;
 518                  $log->backtrace  = format_backtrace($backtrace, true);
 519                  $log->exectime   = $time;
 520                  $log->timelogged = time();
 521                  $this->insert_record('log_queries', $log);
 522              } catch (Exception $ignored) {
 523              }
 524              $this->loggingquery = false;
 525          }
 526      }
 527  
 528      /**
 529       * Returns the time elapsed since the query started.
 530       * @return float Seconds with microseconds
 531       */
 532      protected function query_time() {
 533          return microtime(true) - $this->last_time;
 534      }
 535  
 536      /**
 537       * Returns database server info array
 538       * @return array Array containing 'description' and 'version' at least.
 539       */
 540      public abstract function get_server_info();
 541  
 542      /**
 543       * Returns supported query parameter types
 544       * @return int bitmask of accepted SQL_PARAMS_*
 545       */
 546      protected abstract function allowed_param_types();
 547  
 548      /**
 549       * Returns the last error reported by the database engine.
 550       * @return string The error message.
 551       */
 552      public abstract function get_last_error();
 553  
 554      /**
 555       * Prints sql debug info
 556       * @param string $sql The query which is being debugged.
 557       * @param array $params The query parameters. (optional)
 558       * @param mixed $obj The library specific object. (optional)
 559       * @return void
 560       */
 561      protected function print_debug($sql, array $params=null, $obj=null) {
 562          if (!$this->get_debug()) {
 563              return;
 564          }
 565          if (CLI_SCRIPT) {
 566              echo "--------------------------------\n";
 567              echo $sql."\n";
 568              if (!is_null($params)) {
 569                  echo "[".var_export($params, true)."]\n";
 570              }
 571              echo "--------------------------------\n";
 572          } else {
 573              echo "<hr />\n";
 574              echo s($sql)."\n";
 575              if (!is_null($params)) {
 576                  echo "[".s(var_export($params, true))."]\n";
 577              }
 578              echo "<hr />\n";
 579          }
 580      }
 581  
 582      /**
 583       * Prints the time a query took to run.
 584       * @return void
 585       */
 586      protected function print_debug_time() {
 587          if (!$this->get_debug()) {
 588              return;
 589          }
 590          $time = $this->query_time();
 591          $message = "Query took: {$time} seconds.\n";
 592          if (CLI_SCRIPT) {
 593              echo $message;
 594              echo "--------------------------------\n";
 595          } else {
 596              echo s($message);
 597              echo "<hr />\n";
 598          }
 599      }
 600  
 601      /**
 602       * Returns the SQL WHERE conditions.
 603       * @param string $table The table name that these conditions will be validated against.
 604       * @param array $conditions The conditions to build the where clause. (must not contain numeric indexes)
 605       * @throws dml_exception
 606       * @return array An array list containing sql 'where' part and 'params'.
 607       */
 608      protected function where_clause($table, array $conditions=null) {
 609          // We accept nulls in conditions
 610          $conditions = is_null($conditions) ? array() : $conditions;
 611  
 612          if (empty($conditions)) {
 613              return array('', array());
 614          }
 615  
 616          // Some checks performed under debugging only
 617          if (debugging()) {
 618              $columns = $this->get_columns($table);
 619              if (empty($columns)) {
 620                  // no supported columns means most probably table does not exist
 621                  throw new dml_exception('ddltablenotexist', $table);
 622              }
 623              foreach ($conditions as $key=>$value) {
 624                  if (!isset($columns[$key])) {
 625                      $a = new stdClass();
 626                      $a->fieldname = $key;
 627                      $a->tablename = $table;
 628                      throw new dml_exception('ddlfieldnotexist', $a);
 629                  }
 630                  $column = $columns[$key];
 631                  if ($column->meta_type == 'X') {
 632                      //ok so the column is a text column. sorry no text columns in the where clause conditions
 633                      throw new dml_exception('textconditionsnotallowed', $conditions);
 634                  }
 635              }
 636          }
 637  
 638          $allowed_types = $this->allowed_param_types();
 639          $where = array();
 640          $params = array();
 641  
 642          foreach ($conditions as $key=>$value) {
 643              if (is_int($key)) {
 644                  throw new dml_exception('invalidnumkey');
 645              }
 646              if (is_null($value)) {
 647                  $where[] = "$key IS NULL";
 648              } else {
 649                  if ($allowed_types & SQL_PARAMS_NAMED) {
 650                      // Need to verify key names because they can contain, originally,
 651                      // spaces and other forbidden chars when using sql_xxx() functions and friends.
 652                      $normkey = trim(preg_replace('/[^a-zA-Z0-9_-]/', '_', $key), '-_');
 653                      if ($normkey !== $key) {
 654                          debugging('Invalid key found in the conditions array.');
 655                      }
 656                      $where[] = "$key = :$normkey";
 657                      $params[$normkey] = $value;
 658                  } else {
 659                      $where[] = "$key = ?";
 660                      $params[] = $value;
 661                  }
 662              }
 663          }
 664          $where = implode(" AND ", $where);
 665          return array($where, $params);
 666      }
 667  
 668      /**
 669       * Returns SQL WHERE conditions for the ..._list group of methods.
 670       *
 671       * @param string $field the name of a field.
 672       * @param array $values the values field might take.
 673       * @return array An array containing sql 'where' part and 'params'
 674       */
 675      protected function where_clause_list($field, array $values) {
 676          if (empty($values)) {
 677              return array("1 = 2", array()); // Fake condition, won't return rows ever. MDL-17645
 678          }
 679  
 680          // Note: Do not use get_in_or_equal() because it can not deal with bools and nulls.
 681  
 682          $params = array();
 683          $select = "";
 684          $values = (array)$values;
 685          foreach ($values as $value) {
 686              if (is_bool($value)) {
 687                  $value = (int)$value;
 688              }
 689              if (is_null($value)) {
 690                  $select = "$field IS NULL";
 691              } else {
 692                  $params[] = $value;
 693              }
 694          }
 695          if ($params) {
 696              if ($select !== "") {
 697                  $select = "$select OR ";
 698              }
 699              $count = count($params);
 700              if ($count == 1) {
 701                  $select = $select."$field = ?";
 702              } else {
 703                  $qs = str_repeat(',?', $count);
 704                  $qs = ltrim($qs, ',');
 705                  $select = $select."$field IN ($qs)";
 706              }
 707          }
 708          return array($select, $params);
 709      }
 710  
 711      /**
 712       * Constructs 'IN()' or '=' sql fragment
 713       * @param mixed $items A single value or array of values for the expression.
 714       * @param int $type Parameter bounding type : SQL_PARAMS_QM or SQL_PARAMS_NAMED.
 715       * @param string $prefix Named parameter placeholder prefix (a unique counter value is appended to each parameter name).
 716       * @param bool $equal True means we want to equate to the constructed expression, false means we don't want to equate to it.
 717       * @param mixed $onemptyitems This defines the behavior when the array of items provided is empty. Defaults to false,
 718       *              meaning throw exceptions. Other values will become part of the returned SQL fragment.
 719       * @throws coding_exception | dml_exception
 720       * @return array A list containing the constructed sql fragment and an array of parameters.
 721       */
 722      public function get_in_or_equal($items, $type=SQL_PARAMS_QM, $prefix='param', $equal=true, $onemptyitems=false) {
 723  
 724          // default behavior, throw exception on empty array
 725          if (is_array($items) and empty($items) and $onemptyitems === false) {
 726              throw new coding_exception('moodle_database::get_in_or_equal() does not accept empty arrays');
 727          }
 728          // handle $onemptyitems on empty array of items
 729          if (is_array($items) and empty($items)) {
 730              if (is_null($onemptyitems)) {             // Special case, NULL value
 731                  $sql = $equal ? ' IS NULL' : ' IS NOT NULL';
 732                  return (array($sql, array()));
 733              } else {
 734                  $items = array($onemptyitems);        // Rest of cases, prepare $items for std processing
 735              }
 736          }
 737  
 738          if ($type == SQL_PARAMS_QM) {
 739              if (!is_array($items) or count($items) == 1) {
 740                  $sql = $equal ? '= ?' : '<> ?';
 741                  $items = (array)$items;
 742                  $params = array_values($items);
 743              } else {
 744                  if ($equal) {
 745                      $sql = 'IN ('.implode(',', array_fill(0, count($items), '?')).')';
 746                  } else {
 747                      $sql = 'NOT IN ('.implode(',', array_fill(0, count($items), '?')).')';
 748                  }
 749                  $params = array_values($items);
 750              }
 751  
 752          } else if ($type == SQL_PARAMS_NAMED) {
 753              if (empty($prefix)) {
 754                  $prefix = 'param';
 755              }
 756  
 757              if (!is_array($items)){
 758                  $param = $prefix.$this->inorequaluniqueindex++;
 759                  $sql = $equal ? "= :$param" : "<> :$param";
 760                  $params = array($param=>$items);
 761              } else if (count($items) == 1) {
 762                  $param = $prefix.$this->inorequaluniqueindex++;
 763                  $sql = $equal ? "= :$param" : "<> :$param";
 764                  $item = reset($items);
 765                  $params = array($param=>$item);
 766              } else {
 767                  $params = array();
 768                  $sql = array();
 769                  foreach ($items as $item) {
 770                      $param = $prefix.$this->inorequaluniqueindex++;
 771                      $params[$param] = $item;
 772                      $sql[] = ':'.$param;
 773                  }
 774                  if ($equal) {
 775                      $sql = 'IN ('.implode(',', $sql).')';
 776                  } else {
 777                      $sql = 'NOT IN ('.implode(',', $sql).')';
 778                  }
 779              }
 780  
 781          } else {
 782              throw new dml_exception('typenotimplement');
 783          }
 784          return array($sql, $params);
 785      }
 786  
 787      /**
 788       * Converts short table name {tablename} to the real prefixed table name in given sql.
 789       * @param string $sql The sql to be operated on.
 790       * @return string The sql with tablenames being prefixed with $CFG->prefix
 791       */
 792      protected function fix_table_names($sql) {
 793          return preg_replace('/\{([a-z][a-z0-9_]*)\}/', $this->prefix.'$1', $sql);
 794      }
 795  
 796      /**
 797       * Internal private utitlity function used to fix parameters.
 798       * Used with {@link preg_replace_callback()}
 799       * @param array $match Refer to preg_replace_callback usage for description.
 800       * @return string
 801       */
 802      private function _fix_sql_params_dollar_callback($match) {
 803          $this->fix_sql_params_i++;
 804          return "\$".$this->fix_sql_params_i;
 805      }
 806  
 807      /**
 808       * Detects object parameters and throws exception if found
 809       * @param mixed $value
 810       * @return void
 811       * @throws coding_exception if object detected
 812       */
 813      protected function detect_objects($value) {
 814          if (is_object($value)) {
 815              throw new coding_exception('Invalid database query parameter value', 'Objects are are not allowed: '.get_class($value));
 816          }
 817      }
 818  
 819      /**
 820       * Normalizes sql query parameters and verifies parameters.
 821       * @param string $sql The query or part of it.
 822       * @param array $params The query parameters.
 823       * @return array (sql, params, type of params)
 824       */
 825      public function fix_sql_params($sql, array $params=null) {
 826          $params = (array)$params; // mke null array if needed
 827          $allowed_types = $this->allowed_param_types();
 828  
 829          // convert table names
 830          $sql = $this->fix_table_names($sql);
 831  
 832          // cast booleans to 1/0 int and detect forbidden objects
 833          foreach ($params as $key => $value) {
 834              $this->detect_objects($value);
 835              $params[$key] = is_bool($value) ? (int)$value : $value;
 836          }
 837  
 838          // NICOLAS C: Fixed regexp for negative backwards look-ahead of double colons. Thanks for Sam Marshall's help
 839          $named_count = preg_match_all('/(?<!:):[a-z][a-z0-9_]*/', $sql, $named_matches); // :: used in pgsql casts
 840          $dollar_count = preg_match_all('/\$[1-9][0-9]*/', $sql, $dollar_matches);
 841          $q_count     = substr_count($sql, '?');
 842  
 843          $count = 0;
 844  
 845          if ($named_count) {
 846              $type = SQL_PARAMS_NAMED;
 847              $count = $named_count;
 848  
 849          }
 850          if ($dollar_count) {
 851              if ($count) {
 852                  throw new dml_exception('mixedtypesqlparam');
 853              }
 854              $type = SQL_PARAMS_DOLLAR;
 855              $count = $dollar_count;
 856  
 857          }
 858          if ($q_count) {
 859              if ($count) {
 860                  throw new dml_exception('mixedtypesqlparam');
 861              }
 862              $type = SQL_PARAMS_QM;
 863              $count = $q_count;
 864  
 865          }
 866  
 867          if (!$count) {
 868               // ignore params
 869              if ($allowed_types & SQL_PARAMS_NAMED) {
 870                  return array($sql, array(), SQL_PARAMS_NAMED);
 871              } else if ($allowed_types & SQL_PARAMS_QM) {
 872                  return array($sql, array(), SQL_PARAMS_QM);
 873              } else {
 874                  return array($sql, array(), SQL_PARAMS_DOLLAR);
 875              }
 876          }
 877  
 878          if ($count > count($params)) {
 879              $a = new stdClass;
 880              $a->expected = $count;
 881              $a->actual = count($params);
 882              throw new dml_exception('invalidqueryparam', $a);
 883          }
 884  
 885          $target_type = $allowed_types;
 886  
 887          if ($type & $allowed_types) { // bitwise AND
 888              if ($count == count($params)) {
 889                  if ($type == SQL_PARAMS_QM) {
 890                      return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based array required
 891                  } else {
 892                      //better do the validation of names below
 893                  }
 894              }
 895              // needs some fixing or validation - there might be more params than needed
 896              $target_type = $type;
 897          }
 898  
 899          if ($type == SQL_PARAMS_NAMED) {
 900              $finalparams = array();
 901              foreach ($named_matches[0] as $key) {
 902                  $key = trim($key, ':');
 903                  if (!array_key_exists($key, $params)) {
 904                      throw new dml_exception('missingkeyinsql', $key, '');
 905                  }
 906                  if (strlen($key) > 30) {
 907                      throw new coding_exception(
 908                              "Placeholder names must be 30 characters or shorter. '" .
 909                              $key . "' is too long.", $sql);
 910                  }
 911                  $finalparams[$key] = $params[$key];
 912              }
 913              if ($count != count($finalparams)) {
 914                  throw new dml_exception('duplicateparaminsql');
 915              }
 916  
 917              if ($target_type & SQL_PARAMS_QM) {
 918                  $sql = preg_replace('/(?<!:):[a-z][a-z0-9_]*/', '?', $sql);
 919                  return array($sql, array_values($finalparams), SQL_PARAMS_QM); // 0-based required
 920              } else if ($target_type & SQL_PARAMS_NAMED) {
 921                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
 922              } else {  // $type & SQL_PARAMS_DOLLAR
 923                  //lambda-style functions eat memory - we use globals instead :-(
 924                  $this->fix_sql_params_i = 0;
 925                  $sql = preg_replace_callback('/(?<!:):[a-z][a-z0-9_]*/', array($this, '_fix_sql_params_dollar_callback'), $sql);
 926                  return array($sql, array_values($finalparams), SQL_PARAMS_DOLLAR); // 0-based required
 927              }
 928  
 929          } else if ($type == SQL_PARAMS_DOLLAR) {
 930              if ($target_type & SQL_PARAMS_DOLLAR) {
 931                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
 932              } else if ($target_type & SQL_PARAMS_QM) {
 933                  $sql = preg_replace('/\$[0-9]+/', '?', $sql);
 934                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
 935              } else { //$target_type & SQL_PARAMS_NAMED
 936                  $sql = preg_replace('/\$([0-9]+)/', ':param\\1', $sql);
 937                  $finalparams = array();
 938                  foreach ($params as $key=>$param) {
 939                      $key++;
 940                      $finalparams['param'.$key] = $param;
 941                  }
 942                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
 943              }
 944  
 945          } else { // $type == SQL_PARAMS_QM
 946              if (count($params) != $count) {
 947                  $params = array_slice($params, 0, $count);
 948              }
 949  
 950              if ($target_type & SQL_PARAMS_QM) {
 951                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
 952              } else if ($target_type & SQL_PARAMS_NAMED) {
 953                  $finalparams = array();
 954                  $pname = 'param0';
 955                  $parts = explode('?', $sql);
 956                  $sql = array_shift($parts);
 957                  foreach ($parts as $part) {
 958                      $param = array_shift($params);
 959                      $pname++;
 960                      $sql .= ':'.$pname.$part;
 961                      $finalparams[$pname] = $param;
 962                  }
 963                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
 964              } else {  // $type & SQL_PARAMS_DOLLAR
 965                  //lambda-style functions eat memory - we use globals instead :-(
 966                  $this->fix_sql_params_i = 0;
 967                  $sql = preg_replace_callback('/\?/', array($this, '_fix_sql_params_dollar_callback'), $sql);
 968                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
 969              }
 970          }
 971      }
 972  
 973      /**
 974       * Ensures that limit params are numeric and positive integers, to be passed to the database.
 975       * We explicitly treat null, '' and -1 as 0 in order to provide compatibility with how limit
 976       * values have been passed historically.
 977       *
 978       * @param int $limitfrom Where to start results from
 979       * @param int $limitnum How many results to return
 980       * @return array Normalised limit params in array($limitfrom, $limitnum)
 981       */
 982      protected function normalise_limit_from_num($limitfrom, $limitnum) {
 983          global $CFG;
 984  
 985          // We explicilty treat these cases as 0.
 986          if ($limitfrom === null || $limitfrom === '' || $limitfrom === -1) {
 987              $limitfrom = 0;
 988          }
 989          if ($limitnum === null || $limitnum === '' || $limitnum === -1) {
 990              $limitnum = 0;
 991          }
 992  
 993          if ($CFG->debugdeveloper) {
 994              if (!is_numeric($limitfrom)) {
 995                  $strvalue = var_export($limitfrom, true);
 996                  debugging("Non-numeric limitfrom parameter detected: $strvalue, did you pass the correct arguments?",
 997                      DEBUG_DEVELOPER);
 998              } else if ($limitfrom < 0) {
 999                  debugging("Negative limitfrom parameter detected: $limitfrom, did you pass the correct arguments?",
1000                      DEBUG_DEVELOPER);
1001              }
1002  
1003              if (!is_numeric($limitnum)) {
1004                  $strvalue = var_export($limitnum, true);
1005                  debugging("Non-numeric limitnum parameter detected: $strvalue, did you pass the correct arguments?",
1006                      DEBUG_DEVELOPER);
1007              } else if ($limitnum < 0) {
1008                  debugging("Negative limitnum parameter detected: $limitnum, did you pass the correct arguments?",
1009                      DEBUG_DEVELOPER);
1010              }
1011          }
1012  
1013          $limitfrom = (int)$limitfrom;
1014          $limitnum  = (int)$limitnum;
1015          $limitfrom = max(0, $limitfrom);
1016          $limitnum  = max(0, $limitnum);
1017  
1018          return array($limitfrom, $limitnum);
1019      }
1020  
1021      /**
1022       * Return tables in database WITHOUT current prefix.
1023       * @param bool $usecache if true, returns list of cached tables.
1024       * @return array of table names in lowercase and without prefix
1025       */
1026      public abstract function get_tables($usecache=true);
1027  
1028      /**
1029       * Return table indexes - everything lowercased.
1030       * @param string $table The table we want to get indexes from.
1031       * @return array An associative array of indexes containing 'unique' flag and 'columns' being indexed
1032       */
1033      public abstract function get_indexes($table);
1034  
1035      /**
1036       * Returns detailed information about columns in table. This information is cached internally.
1037       * @param string $table The table's name.
1038       * @param bool $usecache Flag to use internal cacheing. The default is true.
1039       * @return array of database_column_info objects indexed with column names
1040       */
1041      public abstract function get_columns($table, $usecache=true);
1042  
1043      /**
1044       * Normalise values based on varying RDBMS's dependencies (booleans, LOBs...)
1045       *
1046       * @param database_column_info $column column metadata corresponding with the value we are going to normalise
1047       * @param mixed $value value we are going to normalise
1048       * @return mixed the normalised value
1049       */
1050      protected abstract function normalise_value($column, $value);
1051  
1052      /**
1053       * Resets the internal column details cache
1054       *
1055       * @param array|null $tablenames an array of xmldb table names affected by this request.
1056       * @return void
1057       */
1058      public function reset_caches($tablenames = null) {
1059          if (!empty($tablenames)) {
1060              $dbmetapurged = false;
1061              foreach ($tablenames as $tablename) {
1062                  if ($this->temptables->is_temptable($tablename)) {
1063                      $this->get_temp_tables_cache()->delete($tablename);
1064                  } else if ($dbmetapurged === false) {
1065                      $this->tables = null;
1066                      $this->get_metacache()->purge();
1067                      $this->metacache = null;
1068                      $dbmetapurged = true;
1069                  }
1070              }
1071          } else {
1072              $this->get_temp_tables_cache()->purge();
1073              $this->tables = null;
1074              // Purge MUC as well.
1075              $this->get_metacache()->purge();
1076              $this->metacache = null;
1077          }
1078      }
1079  
1080      /**
1081       * Returns the sql generator used for db manipulation.
1082       * Used mostly in upgrade.php scripts.
1083       * @return database_manager The instance used to perform ddl operations.
1084       * @see lib/ddl/database_manager.php
1085       */
1086      public function get_manager() {
1087          global $CFG;
1088  
1089          if (!$this->database_manager) {
1090              require_once($CFG->libdir.'/ddllib.php');
1091  
1092              $classname = $this->get_dbfamily().'_sql_generator';
1093              require_once("$CFG->libdir/ddl/$classname.php");
1094              $generator = new $classname($this, $this->temptables);
1095  
1096              $this->database_manager = new database_manager($this, $generator);
1097          }
1098          return $this->database_manager;
1099      }
1100  
1101      /**
1102       * Attempts to change db encoding to UTF-8 encoding if possible.
1103       * @return bool True is successful.
1104       */
1105      public function change_db_encoding() {
1106          return false;
1107      }
1108  
1109      /**
1110       * Checks to see if the database is in unicode mode?
1111       * @return bool
1112       */
1113      public function setup_is_unicodedb() {
1114          return true;
1115      }
1116  
1117      /**
1118       * Enable/disable very detailed debugging.
1119       * @param bool $state
1120       * @return void
1121       */
1122      public function set_debug($state) {
1123          $this->debug = $state;
1124      }
1125  
1126      /**
1127       * Returns debug status
1128       * @return bool $state
1129       */
1130      public function get_debug() {
1131          return $this->debug;
1132      }
1133  
1134      /**
1135       * Enable/disable detailed sql logging
1136       *
1137       * @deprecated since Moodle 2.9
1138       */
1139      public function set_logging($state) {
1140          throw new coding_exception('set_logging() can not be used any more.');
1141      }
1142  
1143      /**
1144       * Do NOT use in code, this is for use by database_manager only!
1145       * @param string|array $sql query or array of queries
1146       * @param array|null $tablenames an array of xmldb table names affected by this request.
1147       * @return bool true
1148       * @throws ddl_change_structure_exception A DDL specific exception is thrown for any errors.
1149       */
1150      public abstract function change_database_structure($sql, $tablenames = null);
1151  
1152      /**
1153       * Executes a general sql query. Should be used only when no other method suitable.
1154       * Do NOT use this to make changes in db structure, use database_manager methods instead!
1155       * @param string $sql query
1156       * @param array $params query parameters
1157       * @return bool true
1158       * @throws dml_exception A DML specific exception is thrown for any errors.
1159       */
1160      public abstract function execute($sql, array $params=null);
1161  
1162      /**
1163       * Get a number of records as a moodle_recordset where all the given conditions met.
1164       *
1165       * Selects records from the table $table.
1166       *
1167       * If specified, only records meeting $conditions.
1168       *
1169       * If specified, the results will be sorted as specified by $sort. This
1170       * is added to the SQL as "ORDER BY $sort". Example values of $sort
1171       * might be "time ASC" or "time DESC".
1172       *
1173       * If $fields is specified, only those fields are returned.
1174       *
1175       * Since this method is a little less readable, use of it should be restricted to
1176       * code where it's possible there might be large datasets being returned.  For known
1177       * small datasets use get_records - it leads to simpler code.
1178       *
1179       * If you only want some of the records, specify $limitfrom and $limitnum.
1180       * The query will skip the first $limitfrom records (according to the sort
1181       * order) and then return the next $limitnum records. If either of $limitfrom
1182       * or $limitnum is specified, both must be present.
1183       *
1184       * The return value is a moodle_recordset
1185       * if the query succeeds. If an error occurs, false is returned.
1186       *
1187       * @param string $table the table to query.
1188       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1189       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1190       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1191       * @param int $limitfrom return a subset of records, starting at this point (optional).
1192       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1193       * @return moodle_recordset A moodle_recordset instance
1194       * @throws dml_exception A DML specific exception is thrown for any errors.
1195       */
1196      public function get_recordset($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1197          list($select, $params) = $this->where_clause($table, $conditions);
1198          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1199      }
1200  
1201      /**
1202       * Get a number of records as a moodle_recordset where one field match one list of values.
1203       *
1204       * Only records where $field takes one of the values $values are returned.
1205       * $values must be an array of values.
1206       *
1207       * Other arguments and the return type are like {@link function get_recordset}.
1208       *
1209       * @param string $table the table to query.
1210       * @param string $field a field to check (optional).
1211       * @param array $values array of values the field must have
1212       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1213       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1214       * @param int $limitfrom return a subset of records, starting at this point (optional).
1215       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1216       * @return moodle_recordset A moodle_recordset instance.
1217       * @throws dml_exception A DML specific exception is thrown for any errors.
1218       */
1219      public function get_recordset_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1220          list($select, $params) = $this->where_clause_list($field, $values);
1221          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1222      }
1223  
1224      /**
1225       * Get a number of records as a moodle_recordset which match a particular WHERE clause.
1226       *
1227       * If given, $select is used as the SELECT parameter in the SQL query,
1228       * otherwise all records from the table are returned.
1229       *
1230       * Other arguments and the return type are like {@link function get_recordset}.
1231       *
1232       * @param string $table the table to query.
1233       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1234       * @param array $params array of sql parameters
1235       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1236       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1237       * @param int $limitfrom return a subset of records, starting at this point (optional).
1238       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1239       * @return moodle_recordset A moodle_recordset instance.
1240       * @throws dml_exception A DML specific exception is thrown for any errors.
1241       */
1242      public function get_recordset_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1243          $sql = "SELECT $fields FROM {".$table."}";
1244          if ($select) {
1245              $sql .= " WHERE $select";
1246          }
1247          if ($sort) {
1248              $sql .= " ORDER BY $sort";
1249          }
1250          return $this->get_recordset_sql($sql, $params, $limitfrom, $limitnum);
1251      }
1252  
1253      /**
1254       * Get a number of records as a moodle_recordset using a SQL statement.
1255       *
1256       * Since this method is a little less readable, use of it should be restricted to
1257       * code where it's possible there might be large datasets being returned.  For known
1258       * small datasets use get_records_sql - it leads to simpler code.
1259       *
1260       * The return type is like {@link function get_recordset}.
1261       *
1262       * @param string $sql the SQL select query to execute.
1263       * @param array $params array of sql parameters
1264       * @param int $limitfrom return a subset of records, starting at this point (optional).
1265       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1266       * @return moodle_recordset A moodle_recordset instance.
1267       * @throws dml_exception A DML specific exception is thrown for any errors.
1268       */
1269      public abstract function get_recordset_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1270  
1271      /**
1272       * Get all records from a table.
1273       *
1274       * This method works around potential memory problems and may improve performance,
1275       * this method may block access to table until the recordset is closed.
1276       *
1277       * @param string $table Name of database table.
1278       * @return moodle_recordset A moodle_recordset instance {@link function get_recordset}.
1279       * @throws dml_exception A DML specific exception is thrown for any errors.
1280       */
1281      public function export_table_recordset($table) {
1282          return $this->get_recordset($table, array());
1283      }
1284  
1285      /**
1286       * Get a number of records as an array of objects where all the given conditions met.
1287       *
1288       * If the query succeeds and returns at least one record, the
1289       * return value is an array of objects, one object for each
1290       * record found. The array key is the value from the first
1291       * column of the result set. The object associated with that key
1292       * has a member variable for each column of the results.
1293       *
1294       * @param string $table the table to query.
1295       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1296       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1297       * @param string $fields a comma separated list of fields to return (optional, by default
1298       *   all fields are returned). The first field will be used as key for the
1299       *   array so must be a unique field such as 'id'.
1300       * @param int $limitfrom return a subset of records, starting at this point (optional).
1301       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1302       * @return array An array of Objects indexed by first column.
1303       * @throws dml_exception A DML specific exception is thrown for any errors.
1304       */
1305      public function get_records($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1306          list($select, $params) = $this->where_clause($table, $conditions);
1307          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1308      }
1309  
1310      /**
1311       * Get a number of records as an array of objects where one field match one list of values.
1312       *
1313       * Return value is like {@link function get_records}.
1314       *
1315       * @param string $table The database table to be checked against.
1316       * @param string $field The field to search
1317       * @param array $values An array of values
1318       * @param string $sort Sort order (as valid SQL sort parameter)
1319       * @param string $fields A comma separated list of fields to be returned from the chosen table. If specified,
1320       *   the first field should be a unique one such as 'id' since it will be used as a key in the associative
1321       *   array.
1322       * @param int $limitfrom return a subset of records, starting at this point (optional).
1323       * @param int $limitnum return a subset comprising this many records in total (optional).
1324       * @return array An array of objects indexed by first column
1325       * @throws dml_exception A DML specific exception is thrown for any errors.
1326       */
1327      public function get_records_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1328          list($select, $params) = $this->where_clause_list($field, $values);
1329          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1330      }
1331  
1332      /**
1333       * Get a number of records as an array of objects which match a particular WHERE clause.
1334       *
1335       * Return value is like {@link function get_records}.
1336       *
1337       * @param string $table The table to query.
1338       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1339       * @param array $params An array of sql parameters
1340       * @param string $sort An order to sort the results in (optional, a valid SQL ORDER BY parameter).
1341       * @param string $fields A comma separated list of fields to return
1342       *   (optional, by default all fields are returned). The first field will be used as key for the
1343       *   array so must be a unique field such as 'id'.
1344       * @param int $limitfrom return a subset of records, starting at this point (optional).
1345       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1346       * @return array of objects indexed by first column
1347       * @throws dml_exception A DML specific exception is thrown for any errors.
1348       */
1349      public function get_records_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1350          if ($select) {
1351              $select = "WHERE $select";
1352          }
1353          if ($sort) {
1354              $sort = " ORDER BY $sort";
1355          }
1356          return $this->get_records_sql("SELECT $fields FROM {" . $table . "} $select $sort", $params, $limitfrom, $limitnum);
1357      }
1358  
1359      /**
1360       * Get a number of records as an array of objects using a SQL statement.
1361       *
1362       * Return value is like {@link function get_records}.
1363       *
1364       * @param string $sql the SQL select query to execute. The first column of this SELECT statement
1365       *   must be a unique value (usually the 'id' field), as it will be used as the key of the
1366       *   returned array.
1367       * @param array $params array of sql parameters
1368       * @param int $limitfrom return a subset of records, starting at this point (optional).
1369       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1370       * @return array of objects indexed by first column
1371       * @throws dml_exception A DML specific exception is thrown for any errors.
1372       */
1373      public abstract function get_records_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1374  
1375      /**
1376       * Get the first two columns from a number of records as an associative array where all the given conditions met.
1377       *
1378       * Arguments are like {@link function get_recordset}.
1379       *
1380       * If no errors occur the return value
1381       * is an associative whose keys come from the first field of each record,
1382       * and whose values are the corresponding second fields.
1383       * False is returned if an error occurs.
1384       *
1385       * @param string $table the table to query.
1386       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
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 - the number of fields should be 2!
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 $limitfrom is set).
1391       * @return array an associative array
1392       * @throws dml_exception A DML specific exception is thrown for any errors.
1393       */
1394      public function get_records_menu($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1395          $menu = array();
1396          if ($records = $this->get_records($table, $conditions, $sort, $fields, $limitfrom, $limitnum)) {
1397              foreach ($records as $record) {
1398                  $record = (array)$record;
1399                  $key   = array_shift($record);
1400                  $value = array_shift($record);
1401                  $menu[$key] = $value;
1402              }
1403          }
1404          return $menu;
1405      }
1406  
1407      /**
1408       * Get the first two columns from a number of records as an associative array which match a particular WHERE clause.
1409       *
1410       * Arguments are like {@link function get_recordset_select}.
1411       * Return value is like {@link function get_records_menu}.
1412       *
1413       * @param string $table The database table to be checked against.
1414       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1415       * @param array $params array of sql parameters
1416       * @param string $sort Sort order (optional) - a valid SQL order parameter
1417       * @param string $fields A comma separated list of fields to be returned from the chosen table - the number of fields should be 2!
1418       * @param int $limitfrom return a subset of records, starting at this point (optional).
1419       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1420       * @return array an associative array
1421       * @throws dml_exception A DML specific exception is thrown for any errors.
1422       */
1423      public function get_records_select_menu($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1424          $menu = array();
1425          if ($records = $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum)) {
1426              foreach ($records as $record) {
1427                  $record = (array)$record;
1428                  $key   = array_shift($record);
1429                  $value = array_shift($record);
1430                  $menu[$key] = $value;
1431              }
1432          }
1433          return $menu;
1434      }
1435  
1436      /**
1437       * Get the first two columns from a number of records as an associative array using a SQL statement.
1438       *
1439       * Arguments are like {@link function get_recordset_sql}.
1440       * Return value is like {@link function get_records_menu}.
1441       *
1442       * @param string $sql The SQL string you wish to be executed.
1443       * @param array $params array of sql parameters
1444       * @param int $limitfrom return a subset of records, starting at this point (optional).
1445       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1446       * @return array an associative array
1447       * @throws dml_exception A DML specific exception is thrown for any errors.
1448       */
1449      public function get_records_sql_menu($sql, array $params=null, $limitfrom=0, $limitnum=0) {
1450          $menu = array();
1451          if ($records = $this->get_records_sql($sql, $params, $limitfrom, $limitnum)) {
1452              foreach ($records as $record) {
1453                  $record = (array)$record;
1454                  $key   = array_shift($record);
1455                  $value = array_shift($record);
1456                  $menu[$key] = $value;
1457              }
1458          }
1459          return $menu;
1460      }
1461  
1462      /**
1463       * Get a single database record as an object where all the given conditions met.
1464       *
1465       * @param string $table The table to select from.
1466       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1467       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1468       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1469       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1470       *                        MUST_EXIST means we will throw an exception if no record or multiple records found.
1471       *
1472       * @todo MDL-30407 MUST_EXIST option should not throw a dml_exception, it should throw a different exception as it's a requested check.
1473       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1474       * @throws dml_exception A DML specific exception is thrown for any errors.
1475       */
1476      public function get_record($table, array $conditions, $fields='*', $strictness=IGNORE_MISSING) {
1477          list($select, $params) = $this->where_clause($table, $conditions);
1478          return $this->get_record_select($table, $select, $params, $fields, $strictness);
1479      }
1480  
1481      /**
1482       * Get a single database record as an object which match a particular WHERE clause.
1483       *
1484       * @param string $table The database table to be checked against.
1485       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1486       * @param array $params array of sql parameters
1487       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1488       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1489       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1490       *                        MUST_EXIST means throw exception if no record or multiple records found
1491       * @return stdClass|false a fieldset object containing the first matching record, false or exception if error not found depending on mode
1492       * @throws dml_exception A DML specific exception is thrown for any errors.
1493       */
1494      public function get_record_select($table, $select, array $params=null, $fields='*', $strictness=IGNORE_MISSING) {
1495          if ($select) {
1496              $select = "WHERE $select";
1497          }
1498          try {
1499              return $this->get_record_sql("SELECT $fields FROM {" . $table . "} $select", $params, $strictness);
1500          } catch (dml_missing_record_exception $e) {
1501              // create new exception which will contain correct table name
1502              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1503          }
1504      }
1505  
1506      /**
1507       * Get a single database record as an object using a SQL statement.
1508       *
1509       * The SQL statement should normally only return one record.
1510       * It is recommended to use get_records_sql() if more matches possible!
1511       *
1512       * @param string $sql The SQL string you wish to be executed, should normally only return one record.
1513       * @param array $params array of sql parameters
1514       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1515       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1516       *                        MUST_EXIST means throw exception if no record or multiple records found
1517       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1518       * @throws dml_exception A DML specific exception is thrown for any errors.
1519       */
1520      public function get_record_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1521          $strictness = (int)$strictness; // we support true/false for BC reasons too
1522          if ($strictness == IGNORE_MULTIPLE) {
1523              $count = 1;
1524          } else {
1525              $count = 0;
1526          }
1527          if (!$records = $this->get_records_sql($sql, $params, 0, $count)) {
1528              // not found
1529              if ($strictness == MUST_EXIST) {
1530                  throw new dml_missing_record_exception('', $sql, $params);
1531              }
1532              return false;
1533          }
1534  
1535          if (count($records) > 1) {
1536              if ($strictness == MUST_EXIST) {
1537                  throw new dml_multiple_records_exception($sql, $params);
1538              }
1539              debugging('Error: mdb->get_record() found more than one record!');
1540          }
1541  
1542          $return = reset($records);
1543          return $return;
1544      }
1545  
1546      /**
1547       * Get a single field value from a table record where all the given conditions met.
1548       *
1549       * @param string $table the table to query.
1550       * @param string $return the field to return the value of.
1551       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1552       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1553       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1554       *                        MUST_EXIST means throw exception if no record or multiple records found
1555       * @return mixed the specified value false if not found
1556       * @throws dml_exception A DML specific exception is thrown for any errors.
1557       */
1558      public function get_field($table, $return, array $conditions, $strictness=IGNORE_MISSING) {
1559          list($select, $params) = $this->where_clause($table, $conditions);
1560          return $this->get_field_select($table, $return, $select, $params, $strictness);
1561      }
1562  
1563      /**
1564       * Get a single field value from a table record which match a particular WHERE clause.
1565       *
1566       * @param string $table the table to query.
1567       * @param string $return the field to return the value of.
1568       * @param string $select A fragment of SQL to be used in a where clause returning one row with one column
1569       * @param array $params array of sql parameters
1570       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1571       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1572       *                        MUST_EXIST means throw exception if no record or multiple records found
1573       * @return mixed the specified value false if not found
1574       * @throws dml_exception A DML specific exception is thrown for any errors.
1575       */
1576      public function get_field_select($table, $return, $select, array $params=null, $strictness=IGNORE_MISSING) {
1577          if ($select) {
1578              $select = "WHERE $select";
1579          }
1580          try {
1581              return $this->get_field_sql("SELECT $return FROM {" . $table . "} $select", $params, $strictness);
1582          } catch (dml_missing_record_exception $e) {
1583              // create new exception which will contain correct table name
1584              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1585          }
1586      }
1587  
1588      /**
1589       * Get a single field value (first field) using a SQL statement.
1590       *
1591       * @param string $sql The SQL query returning one row with one column
1592       * @param array $params array of sql parameters
1593       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1594       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1595       *                        MUST_EXIST means throw exception if no record or multiple records found
1596       * @return mixed the specified value false if not found
1597       * @throws dml_exception A DML specific exception is thrown for any errors.
1598       */
1599      public function get_field_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1600          if (!$record = $this->get_record_sql($sql, $params, $strictness)) {
1601              return false;
1602          }
1603  
1604          $record = (array)$record;
1605          return reset($record); // first column
1606      }
1607  
1608      /**
1609       * Selects records and return values of chosen field as an array which match a particular WHERE clause.
1610       *
1611       * @param string $table the table to query.
1612       * @param string $return the field we are intered in
1613       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1614       * @param array $params array of sql parameters
1615       * @return array of values
1616       * @throws dml_exception A DML specific exception is thrown for any errors.
1617       */
1618      public function get_fieldset_select($table, $return, $select, array $params=null) {
1619          if ($select) {
1620              $select = "WHERE $select";
1621          }
1622          return $this->get_fieldset_sql("SELECT $return FROM {" . $table . "} $select", $params);
1623      }
1624  
1625      /**
1626       * Selects records and return values (first field) as an array using a SQL statement.
1627       *
1628       * @param string $sql The SQL query
1629       * @param array $params array of sql parameters
1630       * @return array of values
1631       * @throws dml_exception A DML specific exception is thrown for any errors.
1632       */
1633      public abstract function get_fieldset_sql($sql, array $params=null);
1634  
1635      /**
1636       * Insert new record into database, as fast as possible, no safety checks, lobs not supported.
1637       * @param string $table name
1638       * @param mixed $params data record as object or array
1639       * @param bool $returnid Returns id of inserted record.
1640       * @param bool $bulk true means repeated inserts expected
1641       * @param bool $customsequence true if 'id' included in $params, disables $returnid
1642       * @return bool|int true or new id
1643       * @throws dml_exception A DML specific exception is thrown for any errors.
1644       */
1645      public abstract function insert_record_raw($table, $params, $returnid=true, $bulk=false, $customsequence=false);
1646  
1647      /**
1648       * Insert a record into a table and return the "id" field if required.
1649       *
1650       * Some conversions and safety checks are carried out. Lobs are supported.
1651       * If the return ID isn't required, then this just reports success as true/false.
1652       * $data is an object containing needed data
1653       * @param string $table The database table to be inserted into
1654       * @param object $dataobject A data object with values for one or more fields in the record
1655       * @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.
1656       * @param bool $bulk Set to true is multiple inserts are expected
1657       * @return bool|int true or new id
1658       * @throws dml_exception A DML specific exception is thrown for any errors.
1659       */
1660      public abstract function insert_record($table, $dataobject, $returnid=true, $bulk=false);
1661  
1662      /**
1663       * Insert multiple records into database as fast as possible.
1664       *
1665       * Order of inserts is maintained, but the operation is not atomic,
1666       * use transactions if necessary.
1667       *
1668       * This method is intended for inserting of large number of small objects,
1669       * do not use for huge objects with text or binary fields.
1670       *
1671       * @since Moodle 2.7
1672       *
1673       * @param string $table  The database table to be inserted into
1674       * @param array|Traversable $dataobjects list of objects to be inserted, must be compatible with foreach
1675       * @return void does not return new record ids
1676       *
1677       * @throws coding_exception if data objects have different structure
1678       * @throws dml_exception A DML specific exception is thrown for any errors.
1679       */
1680      public function insert_records($table, $dataobjects) {
1681          if (!is_array($dataobjects) and !($dataobjects instanceof Traversable)) {
1682              throw new coding_exception('insert_records() passed non-traversable object');
1683          }
1684  
1685          $fields = null;
1686          // Note: override in driver if there is a faster way.
1687          foreach ($dataobjects as $dataobject) {
1688              if (!is_array($dataobject) and !is_object($dataobject)) {
1689                  throw new coding_exception('insert_records() passed invalid record object');
1690              }
1691              $dataobject = (array)$dataobject;
1692              if ($fields === null) {
1693                  $fields = array_keys($dataobject);
1694              } else if ($fields !== array_keys($dataobject)) {
1695                  throw new coding_exception('All dataobjects in insert_records() must have the same structure!');
1696              }
1697              $this->insert_record($table, $dataobject, false);
1698          }
1699      }
1700  
1701      /**
1702       * Import a record into a table, id field is required.
1703       * Safety checks are NOT carried out. Lobs are supported.
1704       *
1705       * @param string $table name of database table to be inserted into
1706       * @param object $dataobject A data object with values for one or more fields in the record
1707       * @return bool true
1708       * @throws dml_exception A DML specific exception is thrown for any errors.
1709       */
1710      public abstract function import_record($table, $dataobject);
1711  
1712      /**
1713       * Update record in database, as fast as possible, no safety checks, lobs not supported.
1714       * @param string $table name
1715       * @param mixed $params data record as object or array
1716       * @param bool $bulk True means repeated updates expected.
1717       * @return bool true
1718       * @throws dml_exception A DML specific exception is thrown for any errors.
1719       */
1720      public abstract function update_record_raw($table, $params, $bulk=false);
1721  
1722      /**
1723       * Update a record in a table
1724       *
1725       * $dataobject is an object containing needed data
1726       * Relies on $dataobject having a variable "id" to
1727       * specify the record to update
1728       *
1729       * @param string $table The database table to be checked against.
1730       * @param object $dataobject An object with contents equal to fieldname=>fieldvalue. Must have an entry for 'id' to map to the table specified.
1731       * @param bool $bulk True means repeated updates expected.
1732       * @return bool true
1733       * @throws dml_exception A DML specific exception is thrown for any errors.
1734       */
1735      public abstract function update_record($table, $dataobject, $bulk=false);
1736  
1737      /**
1738       * Set a single field in every table record where all the given conditions met.
1739       *
1740       * @param string $table The database table to be checked against.
1741       * @param string $newfield the field to set.
1742       * @param string $newvalue the value to set the field to.
1743       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1744       * @return bool true
1745       * @throws dml_exception A DML specific exception is thrown for any errors.
1746       */
1747      public function set_field($table, $newfield, $newvalue, array $conditions=null) {
1748          list($select, $params) = $this->where_clause($table, $conditions);
1749          return $this->set_field_select($table, $newfield, $newvalue, $select, $params);
1750      }
1751  
1752      /**
1753       * Set a single field in every table record which match a particular WHERE clause.
1754       *
1755       * @param string $table The database table to be checked against.
1756       * @param string $newfield the field to set.
1757       * @param string $newvalue the value to set the field to.
1758       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1759       * @param array $params array of sql parameters
1760       * @return bool true
1761       * @throws dml_exception A DML specific exception is thrown for any errors.
1762       */
1763      public abstract function set_field_select($table, $newfield, $newvalue, $select, array $params=null);
1764  
1765  
1766      /**
1767       * Count the records in a table where all the given conditions met.
1768       *
1769       * @param string $table The table to query.
1770       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1771       * @return int The count of records returned from the specified criteria.
1772       * @throws dml_exception A DML specific exception is thrown for any errors.
1773       */
1774      public function count_records($table, array $conditions=null) {
1775          list($select, $params) = $this->where_clause($table, $conditions);
1776          return $this->count_records_select($table, $select, $params);
1777      }
1778  
1779      /**
1780       * Count the records in a table which match a particular WHERE clause.
1781       *
1782       * @param string $table The database table to be checked against.
1783       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1784       * @param array $params array of sql parameters
1785       * @param string $countitem The count string to be used in the SQL call. Default is COUNT('x').
1786       * @return int The count of records returned from the specified criteria.
1787       * @throws dml_exception A DML specific exception is thrown for any errors.
1788       */
1789      public function count_records_select($table, $select, array $params=null, $countitem="COUNT('x')") {
1790          if ($select) {
1791              $select = "WHERE $select";
1792          }
1793          return $this->count_records_sql("SELECT $countitem FROM {" . $table . "} $select", $params);
1794      }
1795  
1796      /**
1797       * Get the result of a SQL SELECT COUNT(...) query.
1798       *
1799       * Given a query that counts rows, return that count. (In fact,
1800       * given any query, return the first field of the first record
1801       * returned. However, this method should only be used for the
1802       * intended purpose.) If an error occurs, 0 is returned.
1803       *
1804       * @param string $sql The SQL string you wish to be executed.
1805       * @param array $params array of sql parameters
1806       * @return int the count
1807       * @throws dml_exception A DML specific exception is thrown for any errors.
1808       */
1809      public function count_records_sql($sql, array $params=null) {
1810          $count = $this->get_field_sql($sql, $params);
1811          if ($count === false or !is_number($count) or $count < 0) {
1812              throw new coding_exception("count_records_sql() expects the first field to contain non-negative number from COUNT(), '$count' found instead.");
1813          }
1814          return (int)$count;
1815      }
1816  
1817      /**
1818       * Test whether a record exists in a table where all the given conditions met.
1819       *
1820       * @param string $table The table to check.
1821       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1822       * @return bool true if a matching record exists, else false.
1823       * @throws dml_exception A DML specific exception is thrown for any errors.
1824       */
1825      public function record_exists($table, array $conditions) {
1826          list($select, $params) = $this->where_clause($table, $conditions);
1827          return $this->record_exists_select($table, $select, $params);
1828      }
1829  
1830      /**
1831       * Test whether any records exists in a table which match a particular WHERE clause.
1832       *
1833       * @param string $table The database table to be checked against.
1834       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1835       * @param array $params array of sql parameters
1836       * @return bool true if a matching record exists, else false.
1837       * @throws dml_exception A DML specific exception is thrown for any errors.
1838       */
1839      public function record_exists_select($table, $select, array $params=null) {
1840          if ($select) {
1841              $select = "WHERE $select";
1842          }
1843          return $this->record_exists_sql("SELECT 'x' FROM {" . $table . "} $select", $params);
1844      }
1845  
1846      /**
1847       * Test whether a SQL SELECT statement returns any records.
1848       *
1849       * This function returns true if the SQL statement executes
1850       * without any errors and returns at least one record.
1851       *
1852       * @param string $sql The SQL statement to execute.
1853       * @param array $params array of sql parameters
1854       * @return bool true if the SQL executes without errors and returns at least one record.
1855       * @throws dml_exception A DML specific exception is thrown for any errors.
1856       */
1857      public function record_exists_sql($sql, array $params=null) {
1858          $mrs = $this->get_recordset_sql($sql, $params, 0, 1);
1859          $return = $mrs->valid();
1860          $mrs->close();
1861          return $return;
1862      }
1863  
1864      /**
1865       * Delete the records from a table where all the given conditions met.
1866       * If conditions not specified, table is truncated.
1867       *
1868       * @param string $table the table to delete from.
1869       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1870       * @return bool true.
1871       * @throws dml_exception A DML specific exception is thrown for any errors.
1872       */
1873      public function delete_records($table, array $conditions=null) {
1874          // truncate is drop/create (DDL), not transactional safe,
1875          // so we don't use the shortcut within them. MDL-29198
1876          if (is_null($conditions) && empty($this->transactions)) {
1877              return $this->execute("TRUNCATE TABLE {".$table."}");
1878          }
1879          list($select, $params) = $this->where_clause($table, $conditions);
1880          return $this->delete_records_select($table, $select, $params);
1881      }
1882  
1883      /**
1884       * Delete the records from a table where one field match one list of values.
1885       *
1886       * @param string $table the table to delete from.
1887       * @param string $field The field to search
1888       * @param array $values array of values
1889       * @return bool true.
1890       * @throws dml_exception A DML specific exception is thrown for any errors.
1891       */
1892      public function delete_records_list($table, $field, array $values) {
1893          list($select, $params) = $this->where_clause_list($field, $values);
1894          return $this->delete_records_select($table, $select, $params);
1895      }
1896  
1897      /**
1898       * Delete one or more records from a table which match a particular WHERE clause.
1899       *
1900       * @param string $table The database table to be checked against.
1901       * @param string $select A fragment of SQL to be used in a where clause in the SQL call (used to define the selection criteria).
1902       * @param array $params array of sql parameters
1903       * @return bool true.
1904       * @throws dml_exception A DML specific exception is thrown for any errors.
1905       */
1906      public abstract function delete_records_select($table, $select, array $params=null);
1907  
1908      /**
1909       * Returns the FROM clause required by some DBs in all SELECT statements.
1910       *
1911       * To be used in queries not having FROM clause to provide cross_db
1912       * Most DBs don't need it, hence the default is ''
1913       * @return string
1914       */
1915      public function sql_null_from_clause() {
1916          return '';
1917      }
1918  
1919      /**
1920       * Returns the SQL text to be used in order to perform one bitwise AND operation
1921       * between 2 integers.
1922       *
1923       * NOTE: The SQL result is a number and can not be used directly in
1924       *       SQL condition, please compare it to some number to get a bool!!
1925       *
1926       * @param int $int1 First integer in the operation.
1927       * @param int $int2 Second integer in the operation.
1928       * @return string The piece of SQL code to be used in your statement.
1929       */
1930      public function sql_bitand($int1, $int2) {
1931          return '((' . $int1 . ') & (' . $int2 . '))';
1932      }
1933  
1934      /**
1935       * Returns the SQL text to be used in order to perform one bitwise NOT operation
1936       * with 1 integer.
1937       *
1938       * @param int $int1 The operand integer in the operation.
1939       * @return string The piece of SQL code to be used in your statement.
1940       */
1941      public function sql_bitnot($int1) {
1942          return '(~(' . $int1 . '))';
1943      }
1944  
1945      /**
1946       * Returns the SQL text to be used in order to perform one bitwise OR operation
1947       * between 2 integers.
1948       *
1949       * NOTE: The SQL result is a number and can not be used directly in
1950       *       SQL condition, please compare it to some number to get a bool!!
1951       *
1952       * @param int $int1 The first operand integer in the operation.
1953       * @param int $int2 The second operand integer in the operation.
1954       * @return string The piece of SQL code to be used in your statement.
1955       */
1956      public function sql_bitor($int1, $int2) {
1957          return '((' . $int1 . ') | (' . $int2 . '))';
1958      }
1959  
1960      /**
1961       * Returns the SQL text to be used in order to perform one bitwise XOR operation
1962       * between 2 integers.
1963       *
1964       * NOTE: The SQL result is a number and can not be used directly in
1965       *       SQL condition, please compare it to some number to get a bool!!
1966       *
1967       * @param int $int1 The first operand integer in the operation.
1968       * @param int $int2 The second operand integer in the operation.
1969       * @return string The piece of SQL code to be used in your statement.
1970       */
1971      public function sql_bitxor($int1, $int2) {
1972          return '((' . $int1 . ') ^ (' . $int2 . '))';
1973      }
1974  
1975      /**
1976       * Returns the SQL text to be used in order to perform module '%'
1977       * operation - remainder after division
1978       *
1979       * @param int $int1 The first operand integer in the operation.
1980       * @param int $int2 The second operand integer in the operation.
1981       * @return string The piece of SQL code to be used in your statement.
1982       */
1983      public function sql_modulo($int1, $int2) {
1984          return '((' . $int1 . ') % (' . $int2 . '))';
1985      }
1986  
1987      /**
1988       * Returns the cross db correct CEIL (ceiling) expression applied to fieldname.
1989       * note: Most DBs use CEIL(), hence it's the default here.
1990       *
1991       * @param string $fieldname The field (or expression) we are going to ceil.
1992       * @return string The piece of SQL code to be used in your ceiling statement.
1993       */
1994      public function sql_ceil($fieldname) {
1995          return ' CEIL(' . $fieldname . ')';
1996      }
1997  
1998      /**
1999       * Returns the SQL to be used in order to CAST one CHAR column to INTEGER.
2000       *
2001       * Be aware that the CHAR column you're trying to cast contains really
2002       * int values or the RDBMS will throw an error!
2003       *
2004       * @param string $fieldname The name of the field to be casted.
2005       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2006       * @return string The piece of SQL code to be used in your statement.
2007       */
2008      public function sql_cast_char2int($fieldname, $text=false) {
2009          return ' ' . $fieldname . ' ';
2010      }
2011  
2012      /**
2013       * Returns the SQL to be used in order to CAST one CHAR column to REAL number.
2014       *
2015       * Be aware that the CHAR column you're trying to cast contains really
2016       * numbers or the RDBMS will throw an error!
2017       *
2018       * @param string $fieldname The name of the field to be casted.
2019       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2020       * @return string The piece of SQL code to be used in your statement.
2021       */
2022      public function sql_cast_char2real($fieldname, $text=false) {
2023          return ' ' . $fieldname . ' ';
2024      }
2025  
2026      /**
2027       * Returns the SQL to be used in order to an UNSIGNED INTEGER column to SIGNED.
2028       *
2029       * (Only MySQL needs this. MySQL things that 1 * -1 = 18446744073709551615
2030       * if the 1 comes from an unsigned column).
2031       *
2032       * @deprecated since 2.3
2033       * @param string $fieldname The name of the field to be cast
2034       * @return string The piece of SQL code to be used in your statement.
2035       */
2036      public function sql_cast_2signed($fieldname) {
2037          return ' ' . $fieldname . ' ';
2038      }
2039  
2040      /**
2041       * Returns the SQL text to be used to compare one TEXT (clob) column with
2042       * one varchar column, because some RDBMS doesn't support such direct
2043       * comparisons.
2044       *
2045       * @param string $fieldname The name of the TEXT field we need to order by
2046       * @param int $numchars Number of chars to use for the ordering (defaults to 32).
2047       * @return string The piece of SQL code to be used in your statement.
2048       */
2049      public function sql_compare_text($fieldname, $numchars=32) {
2050          return $this->sql_order_by_text($fieldname, $numchars);
2051      }
2052  
2053      /**
2054       * Returns 'LIKE' part of a query.
2055       *
2056       * @param string $fieldname Usually the name of the table column.
2057       * @param string $param Usually the bound query parameter (?, :named).
2058       * @param bool $casesensitive Use case sensitive search when set to true (default).
2059       * @param bool $accentsensitive Use accent sensitive search when set to true (default). (not all databases support accent insensitive)
2060       * @param bool $notlike True means "NOT LIKE".
2061       * @param string $escapechar The escape char for '%' and '_'.
2062       * @return string The SQL code fragment.
2063       */
2064      public function sql_like($fieldname, $param, $casesensitive = true, $accentsensitive = true, $notlike = false, $escapechar = '\\') {
2065          if (strpos($param, '%') !== false) {
2066              debugging('Potential SQL injection detected, sql_like() expects bound parameters (? or :named)');
2067          }
2068          $LIKE = $notlike ? 'NOT LIKE' : 'LIKE';
2069          // by default ignore any sensitiveness - each database does it in a different way
2070          return "$fieldname $LIKE $param ESCAPE '$escapechar'";
2071      }
2072  
2073      /**
2074       * Escape sql LIKE special characters like '_' or '%'.
2075       * @param string $text The string containing characters needing escaping.
2076       * @param string $escapechar The desired escape character, defaults to '\\'.
2077       * @return string The escaped sql LIKE string.
2078       */
2079      public function sql_like_escape($text, $escapechar = '\\') {
2080          $text = str_replace('_', $escapechar.'_', $text);
2081          $text = str_replace('%', $escapechar.'%', $text);
2082          return $text;
2083      }
2084  
2085      /**
2086       * Returns the proper SQL to do CONCAT between the elements(fieldnames) passed.
2087       *
2088       * This function accepts variable number of string parameters.
2089       * All strings/fieldnames will used in the SQL concatenate statement generated.
2090       *
2091       * @return string The SQL to concatenate strings passed in.
2092       * @uses func_get_args()  and thus parameters are unlimited OPTIONAL number of additional field names.
2093       */
2094      public abstract function sql_concat();
2095  
2096      /**
2097       * Returns the proper SQL to do CONCAT between the elements passed
2098       * with a given separator
2099       *
2100       * @param string $separator The separator desired for the SQL concatenating $elements.
2101       * @param array  $elements The array of strings to be concatenated.
2102       * @return string The SQL to concatenate the strings.
2103       */
2104      public abstract function sql_concat_join($separator="' '", $elements=array());
2105  
2106      /**
2107       * Returns the proper SQL (for the dbms in use) to concatenate $firstname and $lastname
2108       *
2109       * @todo MDL-31233 This may not be needed here.
2110       *
2111       * @param string $first User's first name (default:'firstname').
2112       * @param string $last User's last name (default:'lastname').
2113       * @return string The SQL to concatenate strings.
2114       */
2115      function sql_fullname($first='firstname', $last='lastname') {
2116          return $this->sql_concat($first, "' '", $last);
2117      }
2118  
2119      /**
2120       * Returns the SQL text to be used to order by one TEXT (clob) column, because
2121       * some RDBMS doesn't support direct ordering of such fields.
2122       *
2123       * Note that the use or queries being ordered by TEXT columns must be minimised,
2124       * because it's really slooooooow.
2125       *
2126       * @param string $fieldname The name of the TEXT field we need to order by.
2127       * @param int $numchars The number of chars to use for the ordering (defaults to 32).
2128       * @return string The piece of SQL code to be used in your statement.
2129       */
2130      public function sql_order_by_text($fieldname, $numchars=32) {
2131          return $fieldname;
2132      }
2133  
2134      /**
2135       * Returns the SQL text to be used to calculate the length in characters of one expression.
2136       * @param string $fieldname The fieldname/expression to calculate its length in characters.
2137       * @return string the piece of SQL code to be used in the statement.
2138       */
2139      public function sql_length($fieldname) {
2140          return ' LENGTH(' . $fieldname . ')';
2141      }
2142  
2143      /**
2144       * Returns the proper substr() SQL text used to extract substrings from DB
2145       * NOTE: this was originally returning only function name
2146       *
2147       * @param string $expr Some string field, no aggregates.
2148       * @param mixed $start Integer or expression evaluating to integer (1 based value; first char has index 1)
2149       * @param mixed $length Optional integer or expression evaluating to integer.
2150       * @return string The sql substring extraction fragment.
2151       */
2152      public function sql_substr($expr, $start, $length=false) {
2153          if (count(func_get_args()) < 2) {
2154              throw new coding_exception('moodle_database::sql_substr() requires at least two parameters', 'Originally this function was only returning name of SQL substring function, it now requires all parameters.');
2155          }
2156          if ($length === false) {
2157              return "SUBSTR($expr, $start)";
2158          } else {
2159              return "SUBSTR($expr, $start, $length)";
2160          }
2161      }
2162  
2163      /**
2164       * Returns the SQL for returning searching one string for the location of another.
2165       *
2166       * Note, there is no guarantee which order $needle, $haystack will be in
2167       * the resulting SQL so when using this method, and both arguments contain
2168       * placeholders, you should use named placeholders.
2169       *
2170       * @param string $needle the SQL expression that will be searched for.
2171       * @param string $haystack the SQL expression that will be searched in.
2172       * @return string The required searching SQL part.
2173       */
2174      public function sql_position($needle, $haystack) {
2175          // Implementation using standard SQL.
2176          return "POSITION(($needle) IN ($haystack))";
2177      }
2178  
2179      /**
2180       * This used to return empty string replacement character.
2181       *
2182       * @deprecated use bound parameter with empty string instead
2183       *
2184       * @return string An empty string.
2185       */
2186      function sql_empty() {
2187          debugging("sql_empty() is deprecated, please use empty string '' as sql parameter value instead", DEBUG_DEVELOPER);
2188          return '';
2189      }
2190  
2191      /**
2192       * Returns the proper SQL to know if one field is empty.
2193       *
2194       * Note that the function behavior strongly relies on the
2195       * parameters passed describing the field so, please,  be accurate
2196       * when specifying them.
2197       *
2198       * Also, note that this function is not suitable to look for
2199       * fields having NULL contents at all. It's all for empty values!
2200       *
2201       * This function should be applied in all the places where conditions of
2202       * the type:
2203       *
2204       *     ... AND fieldname = '';
2205       *
2206       * are being used. Final result for text fields should be:
2207       *
2208       *     ... AND ' . sql_isempty('tablename', 'fieldname', true/false, true);
2209       *
2210       * and for varchar fields result should be:
2211       *
2212       *    ... AND fieldname = :empty; "; $params['empty'] = '';
2213       *
2214       * (see parameters description below)
2215       *
2216       * @param string $tablename Name of the table (without prefix). Not used for now but can be
2217       *                          necessary in the future if we want to use some introspection using
2218       *                          meta information against the DB. /// TODO ///
2219       * @param string $fieldname Name of the field we are going to check
2220       * @param bool $nullablefield For specifying if the field is nullable (true) or no (false) in the DB.
2221       * @param bool $textfield For specifying if it is a text (also called clob) field (true) or a varchar one (false)
2222       * @return string the sql code to be added to check for empty values
2223       */
2224      public function sql_isempty($tablename, $fieldname, $nullablefield, $textfield) {
2225          return " ($fieldname = '') ";
2226      }
2227  
2228      /**
2229       * Returns the proper SQL to know if one field is not empty.
2230       *
2231       * Note that the function behavior strongly relies on the
2232       * parameters passed describing the field so, please,  be accurate
2233       * when specifying them.
2234       *
2235       * This function should be applied in all the places where conditions of
2236       * the type:
2237       *
2238       *     ... AND fieldname != '';
2239       *
2240       * are being used. Final result for text fields should be:
2241       *
2242       *     ... AND ' . sql_isnotempty('tablename', 'fieldname', true/false, true/false);
2243       *
2244       * and for varchar fields result should be:
2245       *
2246       *    ... AND fieldname != :empty; "; $params['empty'] = '';
2247       *
2248       * (see parameters description below)
2249       *
2250       * @param string $tablename Name of the table (without prefix). This is not used for now but can be
2251       *                          necessary in the future if we want to use some introspection using
2252       *                          meta information against the DB.
2253       * @param string $fieldname The name of the field we are going to check.
2254       * @param bool $nullablefield Specifies if the field is nullable (true) or not (false) in the DB.
2255       * @param bool $textfield Specifies if it is a text (also called clob) field (true) or a varchar one (false).
2256       * @return string The sql code to be added to check for non empty values.
2257       */
2258      public function sql_isnotempty($tablename, $fieldname, $nullablefield, $textfield) {
2259          return ' ( NOT ' . $this->sql_isempty($tablename, $fieldname, $nullablefield, $textfield) . ') ';
2260      }
2261  
2262      /**
2263       * Returns true if this database driver supports regex syntax when searching.
2264       * @return bool True if supported.
2265       */
2266      public function sql_regex_supported() {
2267          return false;
2268      }
2269  
2270      /**
2271       * Returns the driver specific syntax (SQL part) for matching regex positively or negatively (inverted matching).
2272       * Eg: 'REGEXP':'NOT REGEXP' or '~*' : '!~*'
2273       * @param bool $positivematch
2274       * @return string or empty if not supported
2275       */
2276      public function sql_regex($positivematch=true) {
2277          return '';
2278      }
2279  
2280      /**
2281       * Returns the SQL that allows to find intersection of two or more queries
2282       *
2283       * @since Moodle 2.8
2284       *
2285       * @param array $selects array of SQL select queries, each of them only returns fields with the names from $fields
2286       * @param string $fields comma-separated list of fields (used only by some DB engines)
2287       * @return string SQL query that will return only values that are present in each of selects
2288       */
2289      public function sql_intersect($selects, $fields) {
2290          if (!count($selects)) {
2291              throw new coding_exception('sql_intersect() requires at least one element in $selects');
2292          } else if (count($selects) == 1) {
2293              return $selects[0];
2294          }
2295          static $aliascnt = 0;
2296          $rv = '('.$selects[0].')';
2297          for ($i = 1; $i < count($selects); $i++) {
2298              $rv .= " INTERSECT (".$selects[$i].')';
2299          }
2300          return $rv;
2301      }
2302  
2303      /**
2304       * Does this driver support tool_replace?
2305       *
2306       * @since Moodle 2.6.1
2307       * @return bool
2308       */
2309      public function replace_all_text_supported() {
2310          return false;
2311      }
2312  
2313      /**
2314       * Replace given text in all rows of column.
2315       *
2316       * @since Moodle 2.6.1
2317       * @param string $table name of the table
2318       * @param database_column_info $column
2319       * @param string $search
2320       * @param string $replace
2321       */
2322      public function replace_all_text($table, database_column_info $column, $search, $replace) {
2323          if (!$this->replace_all_text_supported()) {
2324              return;
2325          }
2326  
2327          // NOTE: override this methods if following standard compliant SQL
2328          //       does not work for your driver.
2329  
2330          $columnname = $column->name;
2331          $sql = "UPDATE {".$table."}
2332                         SET $columnname = REPLACE($columnname, ?, ?)
2333                       WHERE $columnname IS NOT NULL";
2334  
2335          if ($column->meta_type === 'X') {
2336              $this->execute($sql, array($search, $replace));
2337  
2338          } else if ($column->meta_type === 'C') {
2339              if (core_text::strlen($search) < core_text::strlen($replace)) {
2340                  $colsize = $column->max_length;
2341                  $sql = "UPDATE {".$table."}
2342                         SET $columnname = " . $this->sql_substr("REPLACE(" . $columnname . ", ?, ?)", 1, $colsize) . "
2343                       WHERE $columnname IS NOT NULL";
2344              }
2345              $this->execute($sql, array($search, $replace));
2346          }
2347      }
2348  
2349      /**
2350       * Analyze the data in temporary tables to force statistics collection after bulk data loads.
2351       *
2352       * @return void
2353       */
2354      public function update_temp_table_stats() {
2355          $this->temptables->update_stats();
2356      }
2357  
2358      /**
2359       * Checks and returns true if transactions are supported.
2360       *
2361       * It is not responsible to run productions servers
2362       * on databases without transaction support ;-)
2363       *
2364       * Override in driver if needed.
2365       *
2366       * @return bool
2367       */
2368      protected function transactions_supported() {
2369          // protected for now, this might be changed to public if really necessary
2370          return true;
2371      }
2372  
2373      /**
2374       * Returns true if a transaction is in progress.
2375       * @return bool
2376       */
2377      public function is_transaction_started() {
2378          return !empty($this->transactions);
2379      }
2380  
2381      /**
2382       * This is a test that throws an exception if transaction in progress.
2383       * This test does not force rollback of active transactions.
2384       * @return void
2385       * @throws dml_transaction_exception if stansaction active
2386       */
2387      public function transactions_forbidden() {
2388          if ($this->is_transaction_started()) {
2389              throw new dml_transaction_exception('This code can not be excecuted in transaction');
2390          }
2391      }
2392  
2393      /**
2394       * On DBs that support it, switch to transaction mode and begin a transaction
2395       * you'll need to ensure you call allow_commit() on the returned object
2396       * or your changes *will* be lost.
2397       *
2398       * this is _very_ useful for massive updates
2399       *
2400       * Delegated database transactions can be nested, but only one actual database
2401       * transaction is used for the outer-most delegated transaction. This method
2402       * returns a transaction object which you should keep until the end of the
2403       * delegated transaction. The actual database transaction will
2404       * only be committed if all the nested delegated transactions commit
2405       * successfully. If any part of the transaction rolls back then the whole
2406       * thing is rolled back.
2407       *
2408       * @return moodle_transaction
2409       */
2410      public function start_delegated_transaction() {
2411          $transaction = new moodle_transaction($this);
2412          $this->transactions[] = $transaction;
2413          if (count($this->transactions) == 1) {
2414              $this->begin_transaction();
2415          }
2416          return $transaction;
2417      }
2418  
2419      /**
2420       * Driver specific start of real database transaction,
2421       * this can not be used directly in code.
2422       * @return void
2423       */
2424      protected abstract function begin_transaction();
2425  
2426      /**
2427       * Indicates delegated transaction finished successfully.
2428       * The real database transaction is committed only if
2429       * all delegated transactions committed.
2430       * @param moodle_transaction $transaction The transaction to commit
2431       * @return void
2432       * @throws dml_transaction_exception Creates and throws transaction related exceptions.
2433       */
2434      public function commit_delegated_transaction(moodle_transaction $transaction) {
2435          if ($transaction->is_disposed()) {
2436              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2437          }
2438          // mark as disposed so that it can not be used again
2439          $transaction->dispose();
2440  
2441          if (empty($this->transactions)) {
2442              throw new dml_transaction_exception('Transaction not started', $transaction);
2443          }
2444  
2445          if ($this->force_rollback) {
2446              throw new dml_transaction_exception('Tried to commit transaction after lower level rollback', $transaction);
2447          }
2448  
2449          if ($transaction !== $this->transactions[count($this->transactions) - 1]) {
2450              // one incorrect commit at any level rollbacks everything
2451              $this->force_rollback = true;
2452              throw new dml_transaction_exception('Invalid transaction commit attempt', $transaction);
2453          }
2454  
2455          if (count($this->transactions) == 1) {
2456              // only commit the top most level
2457              $this->commit_transaction();
2458          }
2459          array_pop($this->transactions);
2460  
2461          if (empty($this->transactions)) {
2462              \core\event\manager::database_transaction_commited();
2463              \core\message\manager::database_transaction_commited();
2464          }
2465      }
2466  
2467      /**
2468       * Driver specific commit of real database transaction,
2469       * this can not be used directly in code.
2470       * @return void
2471       */
2472      protected abstract function commit_transaction();
2473  
2474      /**
2475       * Call when delegated transaction failed, this rolls back
2476       * all delegated transactions up to the top most level.
2477       *
2478       * In many cases you do not need to call this method manually,
2479       * because all open delegated transactions are rolled back
2480       * automatically if exceptions not caught.
2481       *
2482       * @param moodle_transaction $transaction An instance of a moodle_transaction.
2483       * @param Exception|Throwable $e The related exception/throwable to this transaction rollback.
2484       * @return void This does not return, instead the exception passed in will be rethrown.
2485       */
2486      public function rollback_delegated_transaction(moodle_transaction $transaction, $e) {
2487          if (!($e instanceof Exception) && !($e instanceof Throwable)) {
2488              // PHP7 - we catch Throwables in phpunit but can't use that as the type hint in PHP5.
2489              $e = new \coding_exception("Must be given an Exception or Throwable object!");
2490          }
2491          if ($transaction->is_disposed()) {
2492              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2493          }
2494          // mark as disposed so that it can not be used again
2495          $transaction->dispose();
2496  
2497          // one rollback at any level rollbacks everything
2498          $this->force_rollback = true;
2499  
2500          if (empty($this->transactions) or $transaction !== $this->transactions[count($this->transactions) - 1]) {
2501              // this may or may not be a coding problem, better just rethrow the exception,
2502              // because we do not want to loose the original $e
2503              throw $e;
2504          }
2505  
2506          if (count($this->transactions) == 1) {
2507              // only rollback the top most level
2508              $this->rollback_transaction();
2509          }
2510          array_pop($this->transactions);
2511          if (empty($this->transactions)) {
2512              // finally top most level rolled back
2513              $this->force_rollback = false;
2514              \core\event\manager::database_transaction_rolledback();
2515              \core\message\manager::database_transaction_rolledback();
2516          }
2517          throw $e;
2518      }
2519  
2520      /**
2521       * Driver specific abort of real database transaction,
2522       * this can not be used directly in code.
2523       * @return void
2524       */
2525      protected abstract function rollback_transaction();
2526  
2527      /**
2528       * Force rollback of all delegated transaction.
2529       * Does not throw any exceptions and does not log anything.
2530       *
2531       * This method should be used only from default exception handlers and other
2532       * core code.
2533       *
2534       * @return void
2535       */
2536      public function force_transaction_rollback() {
2537          if ($this->transactions) {
2538              try {
2539                  $this->rollback_transaction();
2540              } catch (dml_exception $e) {
2541                  // ignore any sql errors here, the connection might be broken
2542              }
2543          }
2544  
2545          // now enable transactions again
2546          $this->transactions = array();
2547          $this->force_rollback = false;
2548  
2549          \core\event\manager::database_transaction_rolledback();
2550          \core\message\manager::database_transaction_rolledback();
2551      }
2552  
2553      /**
2554       * Is session lock supported in this driver?
2555       * @return bool
2556       */
2557      public function session_lock_supported() {
2558          return false;
2559      }
2560  
2561      /**
2562       * Obtains the session lock.
2563       * @param int $rowid The id of the row with session record.
2564       * @param int $timeout The maximum allowed time to wait for the lock in seconds.
2565       * @return void
2566       * @throws dml_exception A DML specific exception is thrown for any errors.
2567       */
2568      public function get_session_lock($rowid, $timeout) {
2569          $this->used_for_db_sessions = true;
2570      }
2571  
2572      /**
2573       * Releases the session lock.
2574       * @param int $rowid The id of the row with session record.
2575       * @return void
2576       * @throws dml_exception A DML specific exception is thrown for any errors.
2577       */
2578      public function release_session_lock($rowid) {
2579      }
2580  
2581      /**
2582       * Returns the number of reads done by this database.
2583       * @return int Number of reads.
2584       */
2585      public function perf_get_reads() {
2586          return $this->reads;
2587      }
2588  
2589      /**
2590       * Returns the number of writes done by this database.
2591       * @return int Number of writes.
2592       */
2593      public function perf_get_writes() {
2594          return $this->writes;
2595      }
2596  
2597      /**
2598       * Returns the number of queries done by this database.
2599       * @return int Number of queries.
2600       */
2601      public function perf_get_queries() {
2602          return $this->writes + $this->reads;
2603      }
2604  
2605      /**
2606       * Time waiting for the database engine to finish running all queries.
2607       * @return float Number of seconds with microseconds
2608       */
2609      public function perf_get_queries_time() {
2610          return $this->queriestime;
2611      }
2612  }