includes/cache/CacheKeyHelper.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  * @ingroup Cache
  20  */
  21
  22 namespace MediaWiki\Cache;
  23
  24 use LogicException;
  25 use MediaWiki\Linker\LinkTarget;
  26 use MediaWiki\Page\PageReference;
  27
  28 /**
  29  * Helper class for mapping value objects representing basic entities to cache keys.
  30  *
  31  * Rationale:
  32  * The logic for deriving the cache key should not be in the value object themselves for two reasons:
  33  * Firstly, the value object should not contain knowledge about caching or keys in general.
  34  * Secondly, all implementations of a given interface must have the exact same logic for deriving
  35  * the cache key. Otherwise, caches will break when different implementations are used when
  36  * interacting with a cache.
  37  *
  38  * Furthermore, the logic for deriving cache keys should not be in a service instance: there can
  39  * only ever be one implementation, it must not depend on configuration, and it should never change.
  40  *
  41  * @ingroup Cache
  42  */
  43 abstract class CacheKeyHelper {
  44
  45         /**
  46          * Private constructor to defy instantiation.
  47          * @return never
  48          */
  49         private function __construct() {
  50                 // we should never even get here...
  51                 throw new LogicException( 'Should not instantiate ' . __CLASS__ );
  52         }
  53
  54         /**
  55          * @param LinkTarget|PageReference $page
  56          *
  57          * @return string
  58          */
  59         public static function getKeyForPage( $page ): string {
  60                 return 'ns' . $page->getNamespace() . ':' . $page->getDBkey();
  61         }
  62 }