implement Cache::exists() for various cache backends

fixes #811

framework/yii/caching/DbCache.php

@@ -89,6 +89,35 @@ class DbCache extends Cache
 	}
 
 	/**
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
+	 */
+	public function exists($key)
+	{
+		$key = $this->buildKey($key);
+
+		$query = new Query;
+		$query->select(array('COUNT(*)'))
+			->from($this->cacheTable)
+			->where('[[id]] = :id AND ([[expire]] = 0 OR [[expire]] >' . time() . ')', array(':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

framework/yii/caching/FileCache.php

@@ -59,6 +59,26 @@ class FileCache extends Cache
 	}
 
 	/**
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
+	 */
+	public function exists($key)
+	{
+		$cacheFile = $this->getCacheFile($this->buildKey($key));
+		if (($time = @filemtime($cacheFile)) > time()) {
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	/**
 	 * 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

framework/yii/caching/RedisCache.php

@@ -104,6 +104,21 @@ class RedisCache extends Cache
 	}
 
 	/**
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
+	 */
+	public function exists($key)
+	{
+		return (bool) $this->_connection->executeCommand('EXISTS', array($this->buildKey($key)));
+	}
+
+	/**
 	 * 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

framework/yii/caching/WinCache.php

@@ -8,7 +8,7 @@
 namespace yii\caching;
 
 /**
- * WinCache provides XCache caching in terms of an application component.
+ * WinCache provides Windows Cache caching in terms of an application component.
  *
  * To use this application component, the [WinCache PHP extension](http://www.iis.net/expand/wincacheforphp)
  * must be loaded. Also note that "wincache.ucenabled" should be set to "On" in your php.ini file.
@@ -21,6 +21,22 @@ namespace yii\caching;
 class WinCache extends Cache
 {
 	/**
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
+	 */
+	public function exists($key)
+	{
+		$key = $this->buildKey($key);
+		return wincache_ucache_exists($key);
+	}
+
+	/**
 	 * 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

framework/yii/caching/XCache.php

@@ -22,6 +22,22 @@ namespace yii\caching;
 class XCache extends Cache
 {
 	/**
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
+	 */
+	public function exists($key)
+	{
+		$key = $this->buildKey($key);
+		return xcache_isset($key);
+	}
+
+	/**
 	 * 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