added Cache::exists() to check key existance in cache

framework/yii/caching/ApcCache.php

@@ -21,12 +21,18 @@ namespace yii\caching;
 class ApcCache extends Cache
 {
 	/**
-	 * Checks the existence of a key in APC cache.
+	 * Checks whether a specified key exists in the cache.
-	 * @param string $key the key to be checked.
+	 * This can be faster than getting the value from the cache if the data is big.
-	 * @return boolean if the key exists or not
+	 * 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 $key a key identifying the cached value. This can be a simple string or
+	 * a complex data structure consisting of factors representing the key.
+	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
 	 */
-	public function keyExists($key)
+	public function exists($key)
 	{
+		$key = $this->buildKey($key);
 		return apc_exists($key);
 	}
 

framework/yii/caching/Cache.php

@@ -134,6 +134,25 @@ abstract class Cache extends Component implements \ArrayAccess
 	}
 
 	/**
+	 * 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.
+	 * In case a cache does not support this feature natively, this method will try to simulate it
+	 * but has no performance improvement over getting it.
+	 * 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);
+		$value = $this->getValue($key);
+		return $value !== false;
+	}
+
+	/**
 	 * Retrieves multiple values from cache with the specified keys.
 	 * Some caches (such as memcache, apc) allow retrieving multiple cached values at the same time,
 	 * which may improve the performance. In case a cache does not support this feature natively,

tests/unit/framework/caching/CacheTestCase.php

@@ -91,6 +91,18 @@ abstract class CacheTestCase extends TestCase
 		$this->assertEquals('array_test', $array['array_test']);
 	}
 
+	public function testExists()
+	{
+		$cache = $this->prepare();
+
+		$this->assertTrue($cache->exists('string_test'));
+		// check whether exists affects the value
+		$this->assertEquals('string_test', $cache->get('string_test'));
+
+		$this->assertTrue($cache->exists('number_test'));
+		$this->assertFalse($cache->exists('not_exists'));
+	}
+
 	public function testArrayAccess()
 	{
 		$cache = $this->getCacheInstance();