Dependency.php 3.06 KB
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<?php
/**
 * @link http://www.yiiframework.com/
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 * @copyright Copyright (c) 2008 Yii Software LLC
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 * @license http://www.yiiframework.com/license/
 */

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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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 *
 * @author Qiang Xue <qiang.xue@gmail.com>
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 * @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;
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	/**
	 * @var boolean whether this dependency is reusable or not. True value means that dependent
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	 * data for this cache dependency will be generated only once per request. This allows you
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	 * 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.
	 */
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	public $reusable = false;
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	/**
	 * @var array static storage of cached data for reusable dependencies.
	 */
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	private static $_reusableData = [];
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	/**
	 * @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.
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	 * @param Cache $cache the cache component that is currently evaluating this dependency
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	 */
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	public function evaluateDependency($cache)
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	{
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		if (!$this->reusable) {
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			$this->data = $this->generateDependencyData($cache);
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		} else {
			if ($this->_hash === null) {
				$this->_hash = sha1(serialize($this));
			}
			if (!array_key_exists($this->_hash, self::$_reusableData)) {
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				self::$_reusableData[$this->_hash] = $this->generateDependencyData($cache);
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			}
			$this->data = self::$_reusableData[$this->_hash];
		}
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	}

	/**
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	 * Returns a value indicating whether the dependency has changed.
	 * @param Cache $cache the cache component that is currently evaluating this dependency
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	 * @return boolean whether the dependency has changed.
	 */
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	public function getHasChanged($cache)
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	{
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		if (!$this->reusable) {
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			return $this->generateDependencyData($cache) !== $this->data;
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		} else {
			if ($this->_hash === null) {
				$this->_hash = sha1(serialize($this));
			}
			if (!array_key_exists($this->_hash, self::$_reusableData)) {
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				self::$_reusableData[$this->_hash] = $this->generateDependencyData($cache);
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			}
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			return self::$_reusableData[$this->_hash] !== $this->data;
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		}
	}

	/**
	 * Resets all cached data for reusable dependencies.
	 */
	public static function resetReusableData()
	{
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		self::$_reusableData = [];
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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.
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	 * @param Cache $cache the cache component that is currently evaluating this dependency
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	 * @return mixed the data needed to determine if dependency has been changed.
	 */
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	abstract protected function generateDependencyData($cache);
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}