diff --git a/framework/yii/caching/ZendDataCache.php b/framework/yii/caching/ZendDataCache.php
index 9ff2fd0..7e040f0 100644
--- a/framework/yii/caching/ZendDataCache.php
+++ b/framework/yii/caching/ZendDataCache.php
@@ -21,6 +21,25 @@ namespace yii\caching;
 class ZendDataCache 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.
+	 * 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 !== null;
+	}
+
+	/**
 	 * 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