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Yii原始碼分析之DbCache

DbCache通過將快取資料儲存在資料庫中來實現快取應用程式元件。

預設情況下,DbCache將會話資料儲存在名為“cache”的資料庫表中。必須預先建立此表。可以通過設定$ cacheTable來更改表名

有關DbCache支援的常見快取操作,請參閱yii \ caching \ Cache。

以下示例顯示如何配置應用程式以使用DbCache:

'cache' => [
    'class' => 'yii\caching\DbCache',
    // 'db' => 'mydb',
    // 'cacheTable' => 'my_cache',
]

我們分析下其原始碼:

<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\caching;

use Yii;
use yii\base\InvalidConfigException;
use yii\db\Connection;
use yii\db\PdoValue;
use yii\db\Query;
use yii\di\Instance;

/**
 * DbCache implements a cache application component by storing cached data in a database.
 *
 * By default, DbCache stores session data in a DB table named 'cache'. This table
 * must be pre-created. The table name can be changed by setting [[cacheTable]].
 *
 * Please refer to [[Cache]] for common cache operations that are supported by DbCache.
 *
 * The following example shows how you can configure the application to use DbCache:
 *
 * ```php
 * 'cache' => [
 *     'class' => 'yii\caching\DbCache',
 *     // 'db' => 'mydb',
 *     // 'cacheTable' => 'my_cache',
 * ]
 * ```
 *
 * For more details and usage information on Cache, see the [guide article on caching](guide:caching-overview).
 *
 * @author Qiang Xue <
[email protected]
> * @since 2.0 */ class DbCache extends Cache { /** * @var Connection|array|string the DB connection object or the application component ID of the DB connection. * After the DbCache object is created, if you want to change this property, you should only assign it * with a DB connection object. * Starting from version 2.0.2, this can also be a configuration array for creating the object. */ public $db = 'db'; /** * @var string name of the DB table to store cache content. * The table should be pre-created as follows: * * ```php * CREATE TABLE cache ( * id char(128) NOT NULL PRIMARY KEY, * expire int(11), * data BLOB * ); * ``` * * where 'BLOB' refers to the BLOB-type of your preferred DBMS. Below are the BLOB type * that can be used for some popular DBMS: * * - MySQL: LONGBLOB * - PostgreSQL: BYTEA * - MSSQL: BLOB * * When using DbCache in a production server, we recommend you create a DB index for the 'expire' * column in the cache table to improve the performance. */ public $cacheTable = '{{%cache}}'; /** * @var int the probability (parts per million) that garbage collection (GC) should be performed * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance. * This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all. */ public $gcProbability = 100; /** * Initializes the DbCache component. * This method will initialize the [[db]] property to make sure it refers to a valid DB connection. * @throws InvalidConfigException if [[db]] is invalid. */ public function init() { parent::init(); $this->db = Instance::ensure($this->db, Connection::className()); } /** * Checks whether a specified key exists in the cache. * This can be faster than getting the value from the cache if the data is big. * Note that this method does not check whether the dependency associated * with the cached data, if there is any, has changed. So a call to [[get]] * may return false while exists returns true. * @param mixed $key a key identifying the cached value. This can be a simple string or * a complex data structure consisting of factors representing the key. * @return bool true if a value exists in cache, false if the value is not in the cache or expired. */ public function exists($key) { $key = $this->buildKey($key); $query = new Query(); $query->select(['COUNT(*)']) ->from($this->cacheTable) ->where('[[id]] = :id AND ([[expire]] = 0 OR [[expire]] >' . time() . ')', [':id' => $key]); if ($this->db->enableQueryCache) { // temporarily disable and re-enable query caching $this->db->enableQueryCache = false; $result = $query->createCommand($this->db)->queryScalar(); $this->db->enableQueryCache = true; } else { $result = $query->createCommand($this->db)->queryScalar(); } return $result > 0; } /** * Retrieves a value from cache with a specified key. * This is the implementation of the method declared in the parent class. * @param string $key a unique key identifying the cached value * @return string|false the value stored in cache, false if the value is not in the cache or expired. */ protected function getValue($key) { $query = new Query(); $query->select(['data']) ->from($this->cacheTable) ->where('[[id]] = :id AND ([[expire]] = 0 OR [[expire]] >' . time() . ')', [':id' => $key]); if ($this->db->enableQueryCache) { // temporarily disable and re-enable query caching $this->db->enableQueryCache = false; $result = $query->createCommand($this->db)->queryScalar(); $this->db->enableQueryCache = true; return $result; } return $query->createCommand($this->db)->queryScalar(); } /** * Retrieves multiple values from cache with the specified keys. * @param array $keys a list of keys identifying the cached values * @return array a list of cached values indexed by the keys */ protected function getValues($keys) { if (empty($keys)) { return []; } $query = new Query(); $query->select(['id', 'data']) ->from($this->cacheTable) ->where(['id' => $keys]) ->andWhere('([[expire]] = 0 OR [[expire]] > ' . time() . ')'); if ($this->db->enableQueryCache) { $this->db->enableQueryCache = false; $rows = $query->createCommand($this->db)->queryAll(); $this->db->enableQueryCache = true; } else { $rows = $query->createCommand($this->db)->queryAll(); } $results = []; foreach ($keys as $key) { $results[$key] = false; } foreach ($rows as $row) { if (is_resource($row['data']) && get_resource_type($row['data']) === 'stream') { $results[$row['id']] = stream_get_contents($row['data']); } else { $results[$row['id']] = $row['data']; } } return $results; } /** * Stores a value identified by a key in cache. * This is the implementation of the method declared in the parent class. * * @param string $key the key identifying the value to be cached * @param string $value the value to be cached. Other types (if you have disabled [[serializer]]) cannot be saved. * @param int $duration the number of seconds in which the cached value will expire. 0 means never expire. * @return bool true if the value is successfully stored into cache, false otherwise */ protected function setValue($key, $value, $duration) { try { $this->db->noCache(function (Connection $db) use ($key, $value, $duration) { $db->createCommand()->upsert($this->cacheTable, [ 'id' => $key, 'expire' => $duration > 0 ? $duration + time() : 0, 'data' => new PdoValue($value, \PDO::PARAM_LOB), ])->execute(); }); $this->gc(); return true; } catch (\Exception $e) { Yii::warning("Unable to update or insert cache data: {$e->getMessage()}", __METHOD__); return false; } } /** * Stores a value identified by a key into cache if the cache does not contain this key. * This is the implementation of the method declared in the parent class. * * @param string $key the key identifying the value to be cached * @param string $value the value to be cached. Other types (if you have disabled [[serializer]]) cannot be saved. * @param int $duration the number of seconds in which the cached value will expire. 0 means never expire. * @return bool true if the value is successfully stored into cache, false otherwise */ protected function addValue($key, $value, $duration) { $this->gc(); try { $this->db->noCache(function (Connection $db) use ($key, $value, $duration) { $db->createCommand() ->insert($this->cacheTable, [ 'id' => $key, 'expire' => $duration > 0 ? $duration + time() : 0, 'data' => new PdoValue($value, \PDO::PARAM_LOB), ])->execute(); }); return true; } catch (\Exception $e) { Yii::warning("Unable to insert cache data: {$e->getMessage()}", __METHOD__); return false; } } /** * Deletes a value with the specified key from cache * This is the implementation of the method declared in the parent class. * @param string $key the key of the value to be deleted * @return bool if no error happens during deletion */ protected function deleteValue($key) { $this->db->noCache(function (Connection $db) use ($key) { $db->createCommand() ->delete($this->cacheTable, ['id' => $key]) ->execute(); }); return true; } /** * Removes the expired data values. * @param bool $force whether to enforce the garbage collection regardless of [[gcProbability]]. * Defaults to false, meaning the actual deletion happens with the probability as specified by [[gcProbability]]. */ public function gc($force = false) { if ($force || mt_rand(0, 1000000) < $this->gcProbability) { $this->db->createCommand() ->delete($this->cacheTable, '[[expire]] > 0 AND [[expire]] < ' . time()) ->execute(); } } /** * Deletes all values from cache. * This is the implementation of the method declared in the parent class. * @return bool whether the flush operation was successful. */ protected function flushValues() { $this->db->createCommand() ->delete($this->cacheTable) ->execute(); return true; } }