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CDbCache

Package	system.caching
Inheritance	class CDbCache » CCache » CApplicationComponent » CComponent
Implements	ArrayAccess, ICache, IApplicationComponent
Since	1.0
Version	$Id$
Source Code	framework/caching/CDbCache.php

CDbCache implements a cache application component by storing cached data in a database.

CDbCache stores cache data in a DB table named cacheTableName. If the table does not exist, it will be automatically created. By setting autoCreateCacheTable to false, you can also manually create the DB table.

CDbCache relies on PDO to access database. By default, it will use a SQLite3 database under the application runtime directory. You can also specify connectionID so that it makes use of a DB application component to access database.

See CCache manual for common cache operations that are supported by CDbCache.

Public Properties

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Property	Type	Description	Defined By
autoCreateCacheTable	boolean	whether the cache DB table should be created automatically if it does not exist.	CDbCache
behaviors	array	the behaviors that should be attached to this component.	CApplicationComponent
cacheTableName	string	name of the DB table to store cache content.	CDbCache
connectionID	string	the ID of the CDbConnection application component.	CDbCache
gCProbability	integer	the probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache.	CDbCache
isInitialized	boolean	whether this application component has been initialized (i.e., init() is invoked.	CApplicationComponent
keyPrefix	string	a string prefixed to every cache key so that it is unique.	CCache

Protected Properties

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Property	Type	Description	Defined By
dbConnection	CDbConnection	the DB connection instance	CDbCache

Public Methods

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Method	Description	Defined By
__call()	Calls the named method which is not a class method.	CComponent
__destruct()	Destructor.	CDbCache
__get()	Returns a property value, an event handler list or a behavior based on its name.	CComponent
__isset()	Checks if a property value is null.	CComponent
__set()	Sets value of a component property.	CComponent
__unset()	Sets a component property to be null.	CComponent
add()	Stores a value identified by a key into cache if the cache does not contain this key.	CCache
asa()	Returns the named behavior object.	CComponent
attachBehavior()	Attaches a behavior to this component.	CComponent
attachBehaviors()	Attaches a list of behaviors to the component.	CComponent
attachEventHandler()	Attaches an event handler to an event.	CComponent
canGetProperty()	Determines whether a property can be read.	CComponent
canSetProperty()	Determines whether a property can be set.	CComponent
delete()	Deletes a value with the specified key from cache	CCache
detachBehavior()	Detaches a behavior from the component.	CComponent
detachBehaviors()	Detaches all behaviors from the component.	CComponent
detachEventHandler()	Detaches an existing event handler.	CComponent
disableBehavior()	Disables an attached behavior.	CComponent
disableBehaviors()	Disables all behaviors attached to this component.	CComponent
enableBehavior()	Enables an attached behavior.	CComponent
enableBehaviors()	Enables all behaviors attached to this component.	CComponent
flush()	Deletes all values from cache.	CDbCache
get()	Retrieves a value from cache with a specified key.	CCache
getEventHandlers()	Returns the list of attached event handlers for an event.	CComponent
getGCProbability()	Returns the probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.	CDbCache
getIsInitialized()	Checks whether this application component has been initialized (i.e., init() is invoked.)	CApplicationComponent
hasEvent()	Determines whether an event is defined.	CComponent
hasEventHandler()	Checks whether the named event has attached handlers.	CComponent
hasProperty()	Determines whether a property is defined.	CComponent
init()	Initializes this application component.	CDbCache
mget()	Retrieves multiple values from cache with the specified keys.	CCache
offsetExists()	Returns whether there is a cache entry with a specified key.	CCache
offsetGet()	Retrieves the value from cache with a specified key.	CCache
offsetSet()	Stores the value identified by a key into cache.	CCache
offsetUnset()	Deletes the value with the specified key from cache	CCache
raiseEvent()	Raises an event.	CComponent
set()	Stores a value identified by a key into cache.	CCache
setGCProbability()	Sets the probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance. This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.	CDbCache

Protected Methods

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Method	Description	Defined By
addValue()	Stores a value identified by a key into cache if the cache does not contain this key.	CDbCache
createCacheTable()	Creates the cache DB table.	CDbCache
deleteValue()	Deletes a value with the specified key from cache	CDbCache
gc()	Removes the expired data values.	CDbCache
generateUniqueKey()		CCache
getDbConnection()	Returns the DB connection instance	CDbCache
getValue()	Retrieves a value from cache with a specified key.	CDbCache
getValues()	Retrieves multiple values from cache with the specified keys.	CDbCache
setValue()	Stores a value identified by a key in cache.	CDbCache

Property Details

autoCreateCacheTable property

public boolean $autoCreateCacheTable;

whether the cache DB table should be created automatically if it does not exist. Defaults to true. If you already have the table created, it is recommended you set this property to be false to improve performance.

Method Details

__destruct() method

public void __destruct()

Source Code: framework/caching/CDbCache.php#67 (show)


public function __destruct()
{
    if($this->_db!==null)
        $this->_db->setActive(false);
}

Destructor. Disconnect the db connection.

addValue() method

protected boolean addValue(string $key, string $value, integer $expire)
$key	string	the key identifying the value to be cached
$value	string	the value to be cached
$expire	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

Source Code: framework/caching/CDbCache.php#235 (show)


protected function addValue($key,$value,$expire)
{
    if(!$this->_gced && mt_rand(0,1000000)<$this->_gcProbability)
    {
        $this->gc();
        $this->_gced=true;
    }

    if($expire>0)
        $expire+=time();
    else
        $expire=0;
    $sql="INSERT INTO {$this->cacheTableName} (id,expire,value) VALUES ('$key',$expire,:value)";
    try
    {
        $command=$this->getDbConnection()->createCommand($sql);
        $command->bindValue(':value',$value,PDO::PARAM_LOB);
        $command->execute();
        return true;
    }
    catch(Exception $e)
    {
        return false;
    }
}

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.

createCacheTable() method

protected void createCacheTable(CDbConnection $db, string $tableName)
$db	CDbConnection	the database connection
$tableName	string	the name of the table to be created

Source Code: framework/caching/CDbCache.php#132 (show)


protected function createCacheTable($db,$tableName)
{
    $driver=$db->getDriverName();
    if($driver==='mysql')
        $blob='LONGBLOB';
    else if($driver==='pgsql')
        $blob='BYTEA';
    else
        $blob='BLOB';
    $sql=<<<EOD
CREATE TABLE $tableName
(
id CHAR(128) PRIMARY KEY,
expire INTEGER,
value $blob
)
EOD;
    $db->createCommand($sql)->execute();
}

Creates the cache DB table.

deleteValue() method

protected boolean deleteValue(string $key)
$key	string	the key of the value to be deleted
{return}	boolean	if no error happens during deletion

Source Code: framework/caching/CDbCache.php#267 (show)


protected function deleteValue($key)
{
    $sql="DELETE FROM {$this->cacheTableName} WHERE id='$key'";
    $this->getDbConnection()->createCommand($sql)->execute();
    return true;
}

Deletes a value with the specified key from cache This is the implementation of the method declared in the parent class.

flush() method

public void flush()

Source Code: framework/caching/CDbCache.php#287 (show)


public function flush()
{
    $this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName}")->execute();
    return true;
}

Deletes all values from cache. Be careful of performing this operation if the cache is shared by multiple applications.

gc() method (available since v1.0.11)

protected void gc()

Source Code: framework/caching/CDbCache.php#278 (show)


protected function gc()
{
    $this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName} WHERE expire>0 AND expire<".time())->execute();
}

Removes the expired data values.

getDbConnection() method

protected CDbConnection getDbConnection()
{return}	CDbConnection	the DB connection instance

Source Code: framework/caching/CDbCache.php#156 (show)


protected function getDbConnection()
{
    if($this->_db!==null)
        return $this->_db;
    else if(($id=$this->connectionID)!==null)
    {
        if(($this->_db=Yii::app()->getComponent($id)) instanceof CDbConnection)
            return $this->_db;
        else
            throw new CException(Yii::t('yii','CDbCache.connectionID "{id}" is invalid. Please make sure it refers to the ID of a CDbConnection application component.',
                array('{id}'=>$id)));
    }
    else
    {
        $dbFile=Yii::app()->getRuntimePath().DIRECTORY_SEPARATOR.'cache-'.Yii::getVersion().'.db';
        return $this->_db=new CDbConnection('sqlite:'.$dbFile);
    }
}

getGCProbability() method (available since v1.0.9)

public integer getGCProbability()
{return}	integer	the probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.

Source Code: framework/caching/CDbCache.php#106 (show)


public function getGCProbability()
{
    return $this->_gcProbability;
}

getValue() method

protected string getValue(string $key)
$key	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.

Source Code: framework/caching/CDbCache.php#181 (show)


protected function getValue($key)
{
    $time=time();
    $sql="SELECT value FROM {$this->cacheTableName} WHERE id='$key' AND (expire=0 OR expire>$time)";
    return $this->getDbConnection()->createCommand($sql)->queryScalar();
}

Retrieves a value from cache with a specified key. This is the implementation of the method declared in the parent class.

getValues() method (available since v1.0.8)

protected array getValues(array $keys)
$keys	array	a list of keys identifying the cached values
{return}	array	a list of cached values indexed by the keys

Source Code: framework/caching/CDbCache.php#194 (show)


protected function getValues($keys)
{
    if(empty($keys))
        return array();

    $ids=implode("','",$keys);
    $time=time();
    $sql="SELECT id, value FROM {$this->cacheTableName} WHERE id IN ('$ids') AND (expire=0 OR expire>$time)";
    $rows=$this->getDbConnection()->createCommand($sql)->queryRows();
    $results=array();
    foreach($keys as $key)
        $results[$key]=false;
    foreach($rows as $row)
        $results[$row['id']]=$results[$row['value']];
    return $results;
}

Retrieves multiple values from cache with the specified keys.

init() method

public void init()

Source Code: framework/caching/CDbCache.php#80 (show)


public function init()
{
    parent::init();

    $db=$this->getDbConnection();
    $db->setActive(true);

    if($this->autoCreateCacheTable)
    {
        $sql="DELETE FROM {$this->cacheTableName} WHERE expire>0 AND expire<".time();
        try
        {
            $db->createCommand($sql)->execute();
        }
        catch(Exception $e)
        {
            $this->createCacheTable($db,$this->cacheTableName);
        }
    }
}

Initializes this application component.

This method is required by the IApplicationComponent interface. It ensures the existence of the cache DB table. It also removes expired data items from the cache.

setGCProbability() method (available since v1.0.9)

public void setGCProbability(integer $value)
$value	integer	the probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance. This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.

Source Code: framework/caching/CDbCache.php#117 (show)


public function setGCProbability($value)
{
    $value=(int)$value;
    if($value<0)
        $value=0;
    if($value>1000000)
        $value=1000000;
    $this->_gcProbability=$value;
}

setValue() method

protected boolean setValue(string $key, string $value, integer $expire)
$key	string	the key identifying the value to be cached
$value	string	the value to be cached
$expire	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

Source Code: framework/caching/CDbCache.php#220 (show)


protected function setValue($key,$value,$expire)
{
    $this->deleteValue($key);
    return $this->addValue($key,$value,$expire);
}

Stores a value identified by a key in cache. This is the implementation of the method declared in the parent class.