includes/dao/DBAccessObjectUtils.php

   1 <?php
   2 /**
   3  * This file contains database access object related constants.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Helper class for DAO classes
  26  *
  27  * @since 1.26
  28  */
  29 class DBAccessObjectUtils implements IDBAccessObject {
  30         /**
  31          * @param integer $bitfield
  32          * @param integer $flags IDBAccessObject::READ_* constant
  33          * @return bool Bitfield has flag $flag set
  34          */
  35         public static function hasFlags( $bitfield, $flags ) {
  36                 return ( $bitfield & $flags ) == $flags;
  37         }
  38
  39         /**
  40          * Get an appropriate DB index, options, and fallback DB index for a query
  41          *
  42          * The fallback DB index and options are to be used if the entity is not found
  43          * with the initial DB index, typically querying the master DB to avoid lag
  44          *
  45          * @param integer $bitfield Bitfield of IDBAccessObject::READ_* constants
  46          * @return array List of DB indexes and options in this order:
  47          *   - DB_MASTER or DB_REPLICA constant for the initial query
  48          *   - SELECT options array for the initial query
  49          *   - DB_MASTER constant for the fallback query; null if no fallback should happen
  50          *   - SELECT options array for the fallback query; empty if no fallback should happen
  51          */
  52         public static function getDBOptions( $bitfield ) {
  53                 if ( self::hasFlags( $bitfield, self::READ_LATEST_IMMUTABLE ) ) {
  54                         $index = DB_REPLICA; // override READ_LATEST if set
  55                         $fallbackIndex = DB_MASTER;
  56                 } elseif ( self::hasFlags( $bitfield, self::READ_LATEST ) ) {
  57                         $index = DB_MASTER;
  58                         $fallbackIndex = null;
  59                 } else {
  60                         $index = DB_REPLICA;
  61                         $fallbackIndex = null;
  62                 }
  63
  64                 $lockingOptions = [];
  65                 if ( self::hasFlags( $bitfield, self::READ_EXCLUSIVE ) ) {
  66                         $lockingOptions[] = 'FOR UPDATE';
  67                 } elseif ( self::hasFlags( $bitfield, self::READ_LOCKING ) ) {
  68                         $lockingOptions[] = 'LOCK IN SHARE MODE';
  69                 }
  70
  71                 if ( $fallbackIndex !== null ) {
  72                         $options = []; // locks on DB_REPLICA make no sense
  73                         $fallbackOptions = $lockingOptions;
  74                 } else {
  75                         $options = $lockingOptions;
  76                         $fallbackOptions = []; // no fallback
  77                 }
  78
  79                 return [ $index, $options, $fallbackIndex, $fallbackOptions ];
  80         }
  81 }