8 files changed, 358 insertions, 268 deletions
diff --git a/HISTORY b/HISTORY
index 3b18476d..90215edb 100644
--- a/HISTORY
+++ b/HISTORY
@@ -20,6 +20,7 @@ ENH: Ticket#106 - Support for validation on THiddenField (Qiang)
 ENH: Ticket#110 - Support for TVarDump with syntax highlight (Qiang)
 ENH: TDataFieldAccessor can access public class variables (Qiang)
 ENH: TPhpErrorException now shows the actual error lines (Qiang)
+ENH: Refactored cache classes with support for cache dependency (Qiang)
 NEW: TStack component (Qiang)
 NEW: TImageMap control (Qiang)
 NEW: TWizard control (Qiang)
diff --git a/demos/quickstart/protected/application.xml b/demos/quickstart/protected/application.xml
index 0eba3be7..cd6dd01e 100644
--- a/demos/quickstart/protected/application.xml
+++ b/demos/quickstart/protected/application.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <application id="QuickStart" Mode="Debug">
-  <!--<modules>-->
+  <modules>
     <!-- uncomment the following to enable caching
     <module id="cache" class="System.Caching.TSqliteCache" />
     -->
@@ -10,7 +10,7 @@
       <route class="TFileLogRoute" />
     </module>
     -->
-  <!--</modules>-->
+  </modules>
   <paths>
     <using namespace="Application.controls.*" />
   </paths>
diff --git a/framework/Caching/TAPCCache.php b/framework/Caching/TAPCCache.php
index 0ed1d433..4c5f2779 100644
--- a/framework/Caching/TAPCCache.php
+++ b/framework/Caching/TAPCCache.php
@@ -35,118 +35,88 @@
  * cache module. It can be accessed via {@link TApplication::getCache()}.
  *
  * TAPCCache may be configured in application configuration file as follows
+ * <code>
  * <module id="cache" class="System.Caching.TAPCCache" />
+ * </code>
  *
  * @author Alban Hanry <compte_messagerie@hotmail.com>
  * @version $Revision: $  $Date: $
  * @package System.Caching
  * @since 3.0b
  */
-class TAPCCache extends TModule implements ICache
+class TAPCCache extends TCache
 {
    /**
-    * @var boolean if the module is initialized
-    */
-   private $_initialized=false;
-
-   /**
-    * @var string a unique prefix used to identify this cache instance from the others
-    */
-   protected $_prefix=null;
-
-   /**
     * Initializes this module.
     * This method is required by the IModule interface.
     * @param TXmlElement configuration for this module, can be null
     * @throws TConfigurationException if apc extension is not installed or not started, check your php.ini
     */
-   public function init($config)
-   {
+	public function init($config)
+	{
 		if(!extension_loaded('apc'))
 			throw new TConfigurationException('apccache_extension_required');
-		$application=$this->getApplication();
-		$this->_prefix=$application->getUniqueID();
-		$application->setCache($this);
-		$this->_initialized=true;
-   }
-
-   /**
-    * Retrieves a value from cache with a specified key.
-    * @return mixed the value stored in cache, false if the value is not in the cache or expired.
-    */
-   public function get($key)
-   {
-		if(($value=apc_fetch($this->_prefix.$key))!==false)
-			return Prado::unserialize($value);
-		else
-			return $value;
-   }
+		parent::init($config);
+	}
 
-   /**
-    * Stores a value identified by a key into cache.
-    * If the cache already contains such a key, the existing value and
-    * expiration time will be replaced with the new ones.
-    *
-    * @param string the key identifying the value to be cached
-    * @param mixed the value to be cached
-    * @param integer the expiration time of the value,
-    *        0 means never expire,
-    * @return boolean true if the value is successfully stored into cache, false otherwise
-    */
-   public function set($key,$value,$expiry=0)
-   {
-		return apc_store($this->_prefix.$key,Prado::serialize($value),$expiry);
-   }
+	/**
+	 * Retrieves a value from cache with a specified key.
+	 * This is the implementation of the method declared in the parent class.
+	 * @param string a unique key identifying the cached value
+	 * @return string the value stored in cache, false if the value is not in the cache or expired.
+	 */
+	protected function getValue($key)
+	{
+		return apc_fetch($key);
+	}
 
-   /**
-    * Stores a value identified by a key into cache if the cache does not contain this key.
-    * APC does not support this mode. So calling this method will raise an exception.
-    * @param string the key identifying the value to be cached
-    * @param mixed the value to be cached
-    * @param integer the expiration time of the value,
-    *        0 means never expire,
-    * @return boolean true if the value is successfully stored into cache, false otherwise
-    * @throw new TNotSupportedException if this method is invoked
-    */
-   public function add($key,$value,$expiry=0)
-   {
-	   throw new TNotSupportedException('apccache_add_unsupported');
-   }
+	/**
+	 * Stores a value identified by a key in cache.
+	 * This is the implementation of the method declared in the parent class.
+	 *
+	 * @param string the key identifying the value to be cached
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	protected function setValue($key,$value,$expire)
+	{
+		return apc_store($key,$value,$expire);
+	}
 
-   /**
-    * Stores a value identified by a key into cache only if the cache contains this key.
-    * The existing value and expiration time will be overwritten with the new ones.
-    * APC does not support this mode. So calling this method will raise an exception.
-    * @param string the key identifying the value to be cached
-    * @param mixed the value to be cached
-    * @param integer the expiration time of the value,
-    *        0 means never expire,
-    * @return boolean true if the value is successfully stored into cache, false otherwise
-    * @throw new TNotSupportedException if this method is invoked
-    */
-   public function replace($key,$value,$expiry=0)
-   {
-	   throw new TNotSupportedException('apccache_replace_unsupported');
-   }
+	/**
+	 * Stores a value identified by a key into cache if the cache does not contain this key.
+	 * This is the implementation of the method declared in the parent class.
+	 *
+	 * @param string the key identifying the value to be cached
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	protected function addValue($key,$value,$expire)
+	{
+		throw new TNotSupportedException('apccache_add_unsupported');
+	}
 
-   /**
-    * Deletes a value with the specified key from cache
-    * @param string the key of the value to be deleted
-    * @return boolean if no error happens during deletion
-    */
-   public function delete($key)
-   {
-      return apc_delete($this->_prefix.$key);
-   }
-
-   /**
-    * Deletes all values from cache.
-    */
-   public function flush()
-   {
-      return apc_clear_cache('user');
-   }
+	/**
+	 * Deletes a value with the specified key from cache
+	 * This is the implementation of the method declared in the parent class.
+	 * @param string the key of the value to be deleted
+	 * @return boolean if no error happens during deletion
+	 */
+	protected function deleteValue($key)
+	{
+		return apc_delete($key);
+	}
 
+	/**
+	 * Deletes all values from cache.
+	 * Be careful of performing this operation if the cache is shared by multiple applications.
+	 */
+	public function flush()
+	{
+		return apc_clear_cache('user');
+	}
 }
 
 ?>
 \ No newline at end of file
diff --git a/framework/Caching/TCache.php b/framework/Caching/TCache.php
index d246b9d0..859180c9 100644
--- a/framework/Caching/TCache.php
+++ b/framework/Caching/TCache.php
@@ -1,22 +1,105 @@
 <?php
+/**
+ * TCache class file.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @link http://www.pradosoft.com/
+ * @copyright Copyright &copy; 2005 PradoSoft
+ * @license http://www.pradosoft.com/license/
+ * @version $Revision: $  $Date: $
+ * @package System.Web
+ */
 
 /**
- * ICache interface.
+ * TCache class
+ *
+ * TCache is the base class for cache classes with different cache storage implementation.
+ *
+ * TCache implements the interface {@link ICache} with the following methods,
+ * - {@link get} : retrieve the value with a key (if any) from cache
+ * - {@link set} : store the value with a key into cache
+ * - {@link add} : store the value only if cache does not have this key
+ * - {@link delete} : delete the value with the specified key from cache
+ * - {@link flush} : delete all values from cache
+ *
+ * Each value is associated with an expiration time. The {@link get} operation
+ * ensures that any expired value will not be returned. The expiration time by
+ * the number of seconds. A expiration time 0 represents never expire.
  *
- * This interface must be implemented by cache managers.
+ * By definition, cache does not ensure the existence of a value
+ * even if it never expires. Cache is not meant to be an persistent storage.
+ *
+ * Child classes must implement the following methods:
+ * - {@link getValue}
+ * - {@link setValue}
+ * - {@link addValue}
+ * - {@link deleteValue}
+ * and optionally {@link flush}
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @version $Revision: $  $Date: $
  * @package System.Caching
  * @since 3.0
  */
-interface ICache
+abstract class TCache extends TModule implements ICache
 {
+	private $_prefix=null;
+
+	/**
+	 * Initializes the cache module.
+	 * This method initializes the cache key prefix and registers the cache module
+	 * with the application.
+	 * @param TXmlElement the module configuration
+	 */
+	public function init($config)
+	{
+		if($this->_prefix===null)
+			$this->_prefix=$this->getApplication()->getUniqueID();
+		$this->getApplication()->setCache($this);
+	}
+
+	/**
+	 * @return string a unique prefix for the keys of cached values.
+	 * If it is not explicitly set, it will take the value of {@link TApplication::getUniqueID}.
+	 */
+	public function getPrefix()
+	{
+		return $this->_prefix;
+	}
+
+	/**
+	 * @param string a unique prefix for the keys of cached values
+	 */
+	public function setPrefix($value)
+	{
+		$this->_prefix=$value;
+	}
+
+	/**
+	 * @param string a key identifying a value to be cached
+	 * @return sring a key generated from the provided key which ensures the uniqueness across applications
+	 */
+	protected function generateUniqueKey($key)
+	{
+		return md5($this->_prefix.$key);
+	}
+
 	/**
 	 * Retrieves a value from cache with a specified key.
+	 * @param string a key identifying the cached value
 	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
 	 */
-	public function get($id);
+	public function get($id)
+	{
+		if(($value=$this->getValue($this->generateUniqueKey($id)))!==false)
+		{
+			$data=unserialize($value);
+			if(!($data[1] instanceof ICacheDependency) || !$data[1]->getHasChanged())
+				return $data[0];
+		}
+		return false;
+	}
+
 	/**
 	 * Stores a value identified by a key into cache.
 	 * If the cache already contains such a key, the existing value and
@@ -24,65 +107,100 @@ interface ICache
 	 *
 	 * @param string the key identifying the value to be cached
 	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function set($id,$value,$expire=0);
+	public function set($id,$value,$expire=0,$dependency=null)
+	{
+		$data=array($value,$dependency);
+		$expire=($expire<=0)?0:time()+$expire;
+		return $this->setValue($this->generateUniqueKey($id),serialize($data),$expire);
+	}
+
 	/**
 	 * Stores a value identified by a key into cache if the cache does not contain this key.
 	 * Nothing will be done if the cache already contains the key.
 	 * @param string the key identifying the value to be cached
 	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function add($id,$value,$expire=0);
-	/**
-	 * Stores a value identified by a key into cache only if the cache contains this key.
-	 * The existing value and expiration time will be overwritten with the new ones.
-	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
-	 * @return boolean true if the value is successfully stored into cache, false otherwise
-	 */
-	public function replace($id,$value,$expire=0);
+	public function add($id,$value,$expire=0,$dependency=null)
+	{
+		$data=array($value,$dependency);
+		$expire=($expire<=0)?0:time()+$expire;
+		return $this->addValue($this->generateUniqueKey($id),serialize($data),$expire);
+	}
+
 	/**
 	 * Deletes a value with the specified key from cache
 	 * @param string the key of the value to be deleted
 	 * @return boolean if no error happens during deletion
 	 */
-	public function delete($id);
+	public function delete($id)
+	{
+		return $this->deleteValue($this->generateUniqueKey($id));
+	}
+
 	/**
 	 * Deletes all values from cache.
 	 * Be careful of performing this operation if the cache is shared by multiple applications.
+	 * Child classes may implement this method to realize the flush operation.
+	 * @throws TNotSupportedException if this method is not overriden by child classes
 	 */
-	public function flush();
-}
-
-interface IDependency
-{
+	public function flush()
+	{
+		throw new TNotSupportedException('cache_flush_unsupported');
+	}
 
-}
+	/**
+	 * Retrieves a value from cache with a specified key.
+	 * This method should be implemented by child classes to store the data
+	 * in specific cache storage. The uniqueness and dependency are handled
+	 * in {@link get()} already. So only the implementation of data retrieval
+	 * is needed.
+	 * @param string a unique key identifying the cached value
+	 * @return string the value stored in cache, false if the value is not in the cache or expired.
+	 */
+	abstract protected function getValue($key);
 
-class TTimeDependency
-{
-}
+	/**
+	 * Stores a value identified by a key in cache.
+	 * This method should be implemented by child classes to store the data
+	 * in specific cache storage. The uniqueness and dependency are handled
+	 * in {@link set()} already. So only the implementation of data storage
+	 * is needed.
+	 *
+	 * @param string the key identifying the value to be cached
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	abstract protected function setValue($key,$value,$expire);
 
-class TFileDependency
-{
-}
+	/**
+	 * Stores a value identified by a key into cache if the cache does not contain this key.
+	 * This method should be implemented by child classes to store the data
+	 * in specific cache storage. The uniqueness and dependency are handled
+	 * in {@link add()} already. So only the implementation of data storage
+	 * is needed.
+	 *
+	 * @param string the key identifying the value to be cached
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	abstract protected function addValue($key,$value,$expire);
 
-class TDirectoryDependency
-{
+	/**
+	 * Deletes a value with the specified key from cache
+	 * This method should be implemented by child classes to delete the data from actual cache storage.
+	 * @param string the key of the value to be deleted
+	 * @return boolean if no error happens during deletion
+	 */
+	abstract protected function deleteValue($key);
 }
 
 ?>
 \ No newline at end of file
diff --git a/framework/Caching/TMemCache.php b/framework/Caching/TMemCache.php
index f3b3e0cf..4497ad4c 100644
--- a/framework/Caching/TMemCache.php
+++ b/framework/Caching/TMemCache.php
@@ -24,7 +24,6 @@
  * - {@link get} : retrieve the value with a key (if any) from cache
  * - {@link set} : store the value with a key into cache
  * - {@link add} : store the value only if cache does not have this key
- * - {@link replace} : store the value only if cache has this key
  * - {@link delete} : delete the value with the specified key from cache
  * - {@link flush} : delete all values from cache
  *
@@ -53,7 +52,9 @@
  * cache module. It can be accessed via {@link TApplication::getCache()}.
  *
  * TMemCache may be configured in application configuration file as follows
+ * <code>
  * <module id="cache" type="System.Caching.TMemCache" Host="localhost" Port=11211 />
+ * </code>
  * where {@link getHost Host} and {@link getPort Port} are configurable properties
  * of TMemCache.
  *
@@ -111,10 +112,8 @@ class TMemCache extends TModule implements ICache
 		$this->_cache=new Memcache;
 		if($this->_cache->connect($this->_host,$this->_port)===false)
 			throw new TConfigurationException('memcache_connection_failed',$this->_host,$this->_port);
-		$application=$this->getApplication();
-		$this->_prefix=$application->getUniqueID();
-		$application->setCache($this);
 		$this->_initialized=true;
+		parent::init($config);
 	}
 
 	/**
@@ -159,75 +158,52 @@ class TMemCache extends TModule implements ICache
 
 	/**
 	 * Retrieves a value from cache with a specified key.
-	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
+	 * This is the implementation of the method declared in the parent class.
+	 * @param string a unique key identifying the cached value
+	 * @return string the value stored in cache, false if the value is not in the cache or expired.
 	 */
-	public function get($key)
+	protected function getValue($key)
 	{
-		return $this->_cache->get($this->generateUniqueKey($key));
+		return $this->_cache->get($key);
 	}
 
 	/**
-	 * Stores a value identified by a key into cache.
-	 * If the cache already contains such a key, the existing value and
-	 * expiration time will be replaced with the new ones.
-	 *
-	 * Note, avoid using this method whenever possible. Database insertion is
-	 * very expensive. Try using {@link add} instead, which will not store the value
-	 * if the key is already in cache.
+	 * Stores a value identified by a key in cache.
+	 * This is the implementation of the method declared in the parent class.
 	 *
 	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function set($key,$value,$expire=0)
+	protected function setValue($key,$value,$expire)
 	{
-		return $this->_cache->set($this->generateUniqueKey($key),$value,0,$expire);
+		return $this->_cache->set($key,$value,0,$expire);
 	}
 
 	/**
 	 * Stores a value identified by a key into cache if the cache does not contain this key.
-	 * Nothing will be done if the cache already contains the key.
-	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
-	 * @return boolean true if the value is successfully stored into cache, false otherwise
-	 */
-	public function add($key,$value,$expiry=0)
-	{
-		return $this->_cache->add($this->generateUniqueKey($key),$value,0,$expiry);
-	}
-
-	/**
-	 * Stores a value identified by a key into cache only if the cache contains this key.
-	 * The existing value and expiration time will be overwritten with the new ones.
+	 * This is the implementation of the method declared in the parent class.
+	 *
 	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function replace($key,$value,$expiry=0)
+	protected function addValue($key,$value,$expire)
 	{
-		return $this->_cache->replace($this->generateUniqueKey($key),$value,0,$expiry);
+		return $this->_cache->add($key,$value,0,$expire);
 	}
 
 	/**
 	 * Deletes a value with the specified key from cache
+	 * This is the implementation of the method declared in the parent class.
 	 * @param string the key of the value to be deleted
 	 * @return boolean if no error happens during deletion
 	 */
-	public function delete($key)
+	protected function deleteValue($key)
 	{
-		return $this->_cache->delete($this->generateUniqueKey($key));
+		return $this->_cache->delete($key);
 	}
 
 	/**
@@ -238,19 +214,6 @@ class TMemCache extends TModule implements ICache
 	{
 		return $this->_cache->flush();
 	}
-
-	/**
-	 * Generates a unique key based on a given user key.
-	 * This method generates a unique key with the memcache.
-	 * The key is made unique by prefixing with a unique string that is supposed
-	 * to be unique among applications using the same memcache.
-	 * @param string user key
-	 * @param string a unique key
-	 */
-	protected function generateUniqueKey($key)
-	{
-		return md5($this->_prefix.$key);
-	}
 }
 
 ?>
 \ No newline at end of file
diff --git a/framework/Caching/TSqliteCache.php b/framework/Caching/TSqliteCache.php
index 92cc46a6..dc4bf13f 100644
--- a/framework/Caching/TSqliteCache.php
+++ b/framework/Caching/TSqliteCache.php
@@ -25,14 +25,12 @@
  * - {@link get} : retrieve the value with a key (if any) from cache
  * - {@link set} : store the value with a key into cache
  * - {@link add} : store the value only if cache does not have this key
- * - {@link replace} : store the value only if cache has this key
  * - {@link delete} : delete the value with the specified key from cache
  * - {@link flush} : delete all values from cache
  *
  * Each value is associated with an expiration time. The {@link get} operation
- * ensures that any expired value will not be returned. The expiration time can
- * be specified by the number of seconds (maximum 60*60*24*30)
- * or a UNIX timestamp. A expiration time 0 represents never expire.
+ * ensures that any expired value will not be returned. The expiration time by
+ * the number of seconds. A expiration time 0 represents never expire.
  *
  * By definition, cache does not ensure the existence of a value
  * even if it never expires. Cache is not meant to be an persistent storage.
@@ -40,7 +38,7 @@
  * Do not use the same database file for multiple applications using TSqliteCache.
  * Also note, cache is shared by all user sessions of an application.
  *
- * To use this module, the sqlite PHP extension must be loaded. Sqlite extension
+ * To use this module, the sqlite PHP extension must be loaded. Note, Sqlite extension
  * is no longer loaded by default since PHP 5.1.
  *
  * Some usage examples of TSqliteCache are as follows,
@@ -55,8 +53,10 @@
  * If loaded, TSqliteCache will register itself with {@link TApplication} as the
  * cache module. It can be accessed via {@link TApplication::getCache()}.
  *
- * TMemCache may be configured in application configuration file as follows
+ * TSqliteCache may be configured in application configuration file as follows
+ * <code>
  * <module id="cache" type="System.Caching.TSqliteCache" DbFile="Application.Data.site" />
+ * </code>
  * where {@link getDbFile DbFile} is a property specifying the location of the
  * SQLite DB file (in the namespace format).
  *
@@ -65,7 +65,7 @@
  * @package System.Caching
  * @since 3.0
  */
-class TSqliteCache extends TModule implements ICache
+class TSqliteCache extends TCache
 {
 	/**
 	 * name of the table storing cache data
@@ -75,10 +75,6 @@ class TSqliteCache extends TModule implements ICache
 	 * extension of the db file name
 	 */
 	const DB_FILE_EXT='.db';
-	/**
-	 * maximum number of seconds specified as expire
-	 */
-	const EXPIRE_LIMIT=2592000;  // 30 days
 
 	/**
 	 * @var boolean if the module has been initialized
@@ -125,7 +121,7 @@ class TSqliteCache extends TModule implements ICache
 		{
 			if($res->numRows()===0)
 			{
-				if($this->_db->query('CREATE TABLE '.self::CACHE_TABLE.' (key CHAR(128) PRIMARY KEY, value BLOB, serialized INT, expire INT)')===false)
+				if($this->_db->query('CREATE TABLE '.self::CACHE_TABLE.' (key CHAR(128) PRIMARY KEY, value BLOB, expire INT)')===false)
 					throw new TConfigurationException('sqlitecache_table_creation_failed',sqlite_error_string(sqlite_last_error()));
 			}
 		}
@@ -133,7 +129,7 @@ class TSqliteCache extends TModule implements ICache
 			throw new TConfigurationException('sqlitecache_table_creation_failed',sqlite_error_string(sqlite_last_error()));
 		$this->_db->query('DELETE FROM '.self::CACHE_TABLE.' WHERE expire<>0 AND expire<'.time());
 		$this->_initialized=true;
-		$this->getApplication()->setCache($this);
+		parent::init($config);
 	}
 
 	/**
@@ -159,96 +155,58 @@ class TSqliteCache extends TModule implements ICache
 
 	/**
 	 * Retrieves a value from cache with a specified key.
-	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
+	 * This is the implementation of the method declared in the parent class.
+	 * @param string a unique key identifying the cached value
+	 * @return string the value stored in cache, false if the value is not in the cache or expired.
 	 */
-	public function get($key)
+	protected function getValue($key)
 	{
-		$sql='SELECT serialized,value FROM '.self::CACHE_TABLE.' WHERE key=\''.md5($key).'\' AND (expire=0 OR expire>'.time().')';
+		$sql='SELECT value FROM '.self::CACHE_TABLE.' WHERE key=\''.$key.'\' AND (expire=0 OR expire>'.time().')';
 		if(($ret=$this->_db->query($sql))!=false && ($row=$ret->fetch(SQLITE_ASSOC))!==false)
-			return $row['serialized']?Prado::unserialize($row['value']):$row['value'];
+			return $row['value'];
 		else
 			return false;
 	}
 
 	/**
-	 * Stores a value identified by a key into cache.
-	 * If the cache already contains such a key, the existing value and
-	 * expiration time will be replaced with the new ones.
-	 *
-	 * Note, avoid using this method whenever possible. Database insertion is
-	 * very expensive. Try using {@link add} instead, which will not store the value
-	 * if the key is already in cache.
+	 * Stores a value identified by a key in cache.
+	 * This is the implementation of the method declared in the parent class.
 	 *
 	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function set($key,$value,$expire=0)
+	protected function setValue($key,$value,$expire)
 	{
-		$serialized=is_string($value)?0:1;
-		$value1=sqlite_escape_string($serialized?Prado::serialize($value):$value);
-		if($expire && $expire<=self::EXPIRE_LIMIT)
-			$expire=time()+$expire;
-		$sql='REPLACE INTO '.self::CACHE_TABLE.' VALUES(\''.md5($key).'\',\''.$value1.'\','.$serialized.','.$expire.')';
+		$sql='REPLACE INTO '.self::CACHE_TABLE.' VALUES(\''.$key.'\',\''.sqlite_escape_string($value).'\','.$expire.')';
 		return $this->_db->query($sql)!==false;
 	}
 
 	/**
 	 * Stores a value identified by a key into cache if the cache does not contain this key.
-	 * Nothing will be done if the cache already contains the key.
+	 * This is the implementation of the method declared in the parent class.
+	 *
 	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
+	 * @param string the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @return boolean true if the value is successfully stored into cache, false otherwise
 	 */
-	public function add($key,$value,$expire=0)
+	protected function addValue($key,$value,$expire)
 	{
-		$serialized=is_string($value)?0:1;
-		$value1=sqlite_escape_string($serialized?Prado::serialize($value):$value);
-		if($expire && $expire<=self::EXPIRE_LIMIT)
-			$expire=time()+$expire;
-		$sql='INSERT INTO '.self::CACHE_TABLE.' VALUES(\''.md5($key).'\',\''.$value1.'\','.$serialized.','.$expire.')';
+		$sql='INSERT INTO '.self::CACHE_TABLE.' VALUES(\''.$key.'\',\''.sqlite_escape_string($value).'\','.$expire.')';
 		return @$this->_db->query($sql)!==false;
 	}
 
 	/**
-	 * Stores a value identified by a key into cache only if the cache contains this key.
-	 * The existing value and expiration time will be overwritten with the new ones.
-	 * @param string the key identifying the value to be cached
-	 * @param mixed the value to be cached
-	 * @param integer the expiration time of the value,
-	 *        0 means never expire,
-	 *        a number less or equal than 60*60*24*30 means the number of seconds that the value will remain valid.
-	 *        a number greater than 60*60*24*30 means a UNIX timestamp after which the value will expire.
-	 * @return boolean true if the value is successfully stored into cache, false otherwise
-	 */
-	public function replace($key,$value,$expire=0)
-	{
-		$serialized=is_string($value)?0:1;
-		$value1=sqlite_escape_string($serialized?Prado::serialize($value):$value);
-		if($expire && $expire<=self::EXPIRE_LIMIT)
-			$expire=time()+$expire;
-		$sql='UPDATE '.self::CACHE_TABLE.' SET value=\''.$value1.'\', serialized='.$serialized.',expire='.$expire.' WHERE key=\''.md5($key).'\'';
-		$this->_db->query($sql);
-		$ret=$this->_db->query('SELECT serialized FROM '.self::CACHE_TABLE.' WHERE key=\''.md5($key).'\'');
-		return ($ret!=false && $ret->numRows()>0);
-	}
-
-	/**
 	 * Deletes a value with the specified key from cache
+	 * This is the implementation of the method declared in the parent class.
 	 * @param string the key of the value to be deleted
 	 * @return boolean if no error happens during deletion
 	 */
-	public function delete($key)
+	protected function deleteValue($key)
 	{
-		$sql='DELETE FROM '.self::CACHE_TABLE.' WHERE key=\''.md5($key).'\'';
+		$sql='DELETE FROM '.self::CACHE_TABLE.' WHERE key=\''.$key.'\'';
 		return $this->_db->query($sql)!==false;
 	}
 
diff --git a/framework/Web/UI/TThemeManager.php b/framework/Web/UI/TThemeManager.php
index 29b48d90..f2de22f5 100644
--- a/framework/Web/UI/TThemeManager.php
+++ b/framework/Web/UI/TThemeManager.php
@@ -209,17 +209,20 @@ class TTheme extends TApplicationComponent implements ITheme
 	{
 		$this->_themeUrl=$themeUrl;
 		$this->_name=basename($themePath);
+		$cacheValid=false;
+		// TODO: the following needs to be cleaned up (Qiang)
 		if(($cache=$this->getApplication()->getCache())!==null)
 		{
 			$array=$cache->get(self::THEME_CACHE_PREFIX.$themePath);
+			//print_r($array);die('here');
 			if(is_array($array))
 			{
 				list($skins,$cssFiles,$jsFiles,$timestamp)=$array;
-				$cacheValid=true;
 				if($this->getApplication()->getMode()!==TApplication::STATE_PERFORMANCE)
 				{
 					if(($dir=opendir($themePath))===false)
 						throw new TIOException('theme_path_inexistent',$themePath);
+					$cacheValid=true;
 					while(($file=readdir($dir))!==false)
 					{
 						if($file==='.' || $file==='..')
@@ -240,14 +243,18 @@ class TTheme extends TApplicationComponent implements ITheme
 				}
 				else
 				{
+					$cacheValid=true;
 					$this->_cssFiles=$cssFiles;
 					$this->_jsFiles=$jsFiles;
 					$this->_skins=$skins;
 				}
 			}
 		}
-		if($this->_skins===null)
+		if(!$cacheValid)
 		{
+			$this->_cssFiles=array();
+			$this->_jsFiles=array();
+			$this->_skins=array();
 			if(($dir=opendir($themePath))===false)
 				throw new TIOException('theme_path_inexistent',$themePath);
 			while(($file=readdir($dir))!==false)
diff --git a/framework/interfaces.php b/framework/interfaces.php
index f63da347..ca5c77bb 100644
--- a/framework/interfaces.php
+++ b/framework/interfaces.php
@@ -169,4 +169,77 @@ interface IStatePersister
 	public function save($state);
 }
 
+
+/**
+ * ICache interface.
+ *
+ * This interface must be implemented by cache managers.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @version $Revision: $  $Date: $
+ * @package System
+ * @since 3.0
+ */
+interface ICache
+{
+	/**
+	 * Retrieves a value from cache with a specified key.
+	 * @param string a key identifying the cached value
+	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
+	 */
+	public function get($id);
+	/**
+	 * Stores a value identified by a key into cache.
+	 * If the cache already contains such a key, the existing value and
+	 * expiration time will be replaced with the new ones.
+	 *
+	 * @param string the key identifying the value to be cached
+	 * @param mixed the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	public function set($id,$value,$expire=0,$dependency=null);
+	/**
+	 * Stores a value identified by a key into cache if the cache does not contain this key.
+	 * Nothing will be done if the cache already contains the key.
+	 * @param string the key identifying the value to be cached
+	 * @param mixed the value to be cached
+	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
+	 * @param ICacheDependency dependency of the cached item. If the dependency changes, the item is labelled invalid.
+	 * @return boolean true if the value is successfully stored into cache, false otherwise
+	 */
+	public function add($id,$value,$expire=0,$dependency=null);
+	/**
+	 * Deletes a value with the specified key from cache
+	 * @param string the key of the value to be deleted
+	 * @return boolean if no error happens during deletion
+	 */
+	public function delete($id);
+	/**
+	 * Deletes all values from cache.
+	 * Be careful of performing this operation if the cache is shared by multiple applications.
+	 */
+	public function flush();
+}
+
+/**
+ * ICacheDependency interface.
+ *
+ * This interface must be implemented by classes meant to be used as
+ * cache dependencies.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @version $Revision: $  $Date: $
+ * @package System
+ * @since 3.0
+ */
+interface ICacheDependency
+{
+	/**
+	 * @return boolean whether the dependency has changed. Defaults to false.
+	 */
+	public function getHasChanged();
+}
+
 ?>
 \ No newline at end of file