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<?php
/**
* @link http://www.yiiframework.com/
* @copyright Copyright (c) 2008 Yii Software LLC
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* @license http://www.yiiframework.com/license/
*/
namespace yii\caching;
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/**
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* Dependency is the base class for cache dependency classes.
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*
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* Child classes should override its [[generateDependencyData()]] for generating
* the actual dependency data.
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*
* @property boolean $hasChanged Whether the dependency has changed.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @since 2.0
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*/
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abstract class Dependency extends \yii\base\Object
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{
/**
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* @var mixed the dependency data that is saved in cache and later is compared with the
* latest dependency data.
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*/
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public $data;
/**
* @var boolean whether this dependency is reusable or not. True value means that dependent
* data for this cache dependency will be generated only once per request. This allows you
* to use the same cache dependency for multiple separate cache calls while generating the same
* page without an overhead of re-evaluating dependency data each time. Defaults to false.
*/
public $reusable = false;
/**
* @var array static storage of cached data for reusable dependencies.
*/
private static $_reusableData = array();
/**
* @var string a unique hash value for this cache dependency.
*/
private $_hash;
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/**
* Evaluates the dependency by generating and saving the data related with dependency.
* This method is invoked by cache before writing data into it.
* @param Cache $cache the cache component that is currently evaluating this dependency
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*/
public function evaluateDependency($cache)
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{
if (!$this->reusable) {
$this->data = $this->generateDependencyData($cache);
} else {
if ($this->_hash === null) {
$this->_hash = sha1(serialize($this));
}
if (!array_key_exists($this->_hash, self::$_reusableData)) {
self::$_reusableData[$this->_hash] = $this->generateDependencyData($cache);
}
$this->data = self::$_reusableData[$this->_hash];
}
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}
/**
* Returns a value indicating whether the dependency has changed.
* @param Cache $cache the cache component that is currently evaluating this dependency
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* @return boolean whether the dependency has changed.
*/
public function getHasChanged($cache)
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{
if (!$this->reusable) {
return $this->generateDependencyData($cache) !== $this->data;
} else {
if ($this->_hash === null) {
$this->_hash = sha1(serialize($this));
}
if (!array_key_exists($this->_hash, self::$_reusableData)) {
self::$_reusableData[$this->_hash] = $this->generateDependencyData($cache);
}
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return self::$_reusableData[$this->_hash] !== $this->data;
}
}
/**
* Resets all cached data for reusable dependencies.
*/
public static function resetReusableData()
{
self::$_reusableData = array();
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}
/**
* Generates the data needed to determine if dependency has been changed.
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* Derived classes should override this method to generate the actual dependency data.
* @param Cache $cache the cache component that is currently evaluating this dependency
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* @return mixed the data needed to determine if dependency has been changed.
*/
abstract protected function generateDependencyData($cache);
}