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<?php
/**
* CDbCache class file
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @link http://www.yiiframework.com/
* @copyright Copyright &copy; 2008-2011 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/

/**
* CDbCache implements a cache application component by storing cached data in a database.
*
* CDbCache stores cache data in a DB table named {@link cacheTableName}.
* If the table does not exist, it will be automatically created.
* By setting {@link autoCreateCacheTable} to false, you can also manually create the DB table.
*
* CDbCache relies on {@link http://www.php.net/manual/en/ref.pdo.php PDO} to access database.
* By default, it will use a SQLite3 database under the application runtime directory.
* You can also specify {@link connectionID} so that it makes use of
* a DB application component to access database.
*
* See {@link CCache} manual for common cache operations that are supported by CDbCache.
*
* @property integer $gCProbability 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.
* @property CDbConnection $dbConnection The DB connection instance.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Id$
* @package system.caching
* @since 1.0
*/
class CDbCache extends CCache
{
/**
* @var string the ID of the {@link CDbConnection} application component. If not set,
* a SQLite3 database will be automatically created and used. The SQLite database file
* is <code>protected/runtime/cache-YiiVersion.db</code>.
*/
public $connectionID;
/**
* @var string name of the DB table to store cache content. Defaults to 'YiiCache'.
* Note, if {@link autoCreateCacheTable} is false and you want to create the DB table
* manually by yourself, you need to make sure the DB table is of the following structure:
* <pre>
* (id CHAR(128) PRIMARY KEY, expire INTEGER, value BLOB)
* </pre>
* Note, some DBMS might not support BLOB type. In this case, replace 'BLOB' with a suitable
* binary data type (e.g. LONGBLOB in MySQL, BYTEA in PostgreSQL.)
* @see autoCreateCacheTable
*/
public $cacheTableName='YiiCache';
/**
* @var boolean 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.
* @see cacheTableName
*/
public $autoCreateCacheTable=true;
/**
* @var CDbConnection the DB connection instance
*/
private $_db;
private $_gcProbability=100;
private $_gced=false;

/**
* Initializes this application component.
*
* This method is required by the {@link IApplicationComponent} interface.
* It ensures the existence of the cache DB table.
* It also removes expired data items from the cache.
*/
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);
}
}
}

/**
* @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.
*/
public function getGCProbability()
{
return $this->_gcProbability;
}

/**
* @param integer $value the probability (parts per million) that garbage collection (GC) should be performed
* when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
* This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.
*/
public function setGCProbability($value)
{
$value=(int)$value;
if($value<0)
$value=0;
if($value>1000000)
$value=1000000;
$this->_gcProbability=$value;
}

/**
* Creates the cache DB table.
* @param CDbConnection $db the database connection
* @param string $tableName the name of the table to be created
*/
protected function createCacheTable($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();
}

/**
* @return CDbConnection the DB connection instance
* @throws CException if {@link connectionID} does not point to a valid application component.
*/
public 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);
}
}

/**
* Sets the DB connection used by the cache component.
* @param CDbConnection $value the DB connection instance
* @since 1.1.5
*/
public function setDbConnection($value)
{
$this->_db=$value;
}

/**
* Retrieves a value from cache with a specified key.
* This is the implementation of the method declared in the parent class.
* @param string $key a unique key identifying the cached value
* @return string the value stored in cache, false if the value is not in the cache or expired.
*/
protected function getValue($key)
{
$time=time();
$sql="SELECT value FROM {$this->cacheTableName} WHERE id='$key' AND (expire=0 OR expire>$time)";
$db=$this->getDbConnection();
if($db->queryCachingDuration>0)
{
$duration=$db->queryCachingDuration;
$db->queryCachingDuration=0;
$result=$db->createCommand($sql)->queryScalar();
$db->queryCachingDuration=$duration;
return $result;
}
else
return $db->createCommand($sql)->queryScalar();
}

/**
* Retrieves multiple values from cache with the specified keys.
* @param array $keys a list of keys identifying the cached values
* @return array a list of cached values indexed by the keys
*/
protected function getValues($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)";

$db=$this->getDbConnection();
if($db->queryCachingDuration>0)
{
$duration=$db->queryCachingDuration;
$db->queryCachingDuration=0;
$rows=$db->createCommand($sql)->queryAll();
$db->queryCachingDuration=$duration;
}
else
$rows=$db->createCommand($sql)->queryAll();

$results=array();
foreach($keys as $key)
$results[$key]=false;
foreach($rows as $row)
$results[$row['id']]=$row['value'];
return $results;
}

/**
* Stores a value identified by a key in cache.
* This is the implementation of the method declared in the parent class.
*
* @param string $key the key identifying the value to be cached
* @param string $value the value to be cached
* @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
protected function setValue($key,$value,$expire)
{
$this->deleteValue($key);
return $this->addValue($key,$value,$expire);
}

/**
* 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 $key the key identifying the value to be cached
* @param string $value the value to be cached
* @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
* @return boolean true if the value is successfully stored into cache, false otherwise
*/
protected function addValue($key,$value,$expire)
{
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;
}
}

/**
* Deletes a value with the specified key from cache
* This is the implementation of the method declared in the parent class.
* @param string $key the key of the value to be deleted
* @return boolean if no error happens during deletion
*/
protected function deleteValue($key)
{
$sql="DELETE FROM {$this->cacheTableName} WHERE id='$key'";
$this->getDbConnection()->createCommand($sql)->execute();
return true;
}

/**
* Removes the expired data values.
*/
protected function gc()
{
$this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName} WHERE expire>0 AND expire<".time())->execute();
}

/**
* Deletes all values from cache.
* This is the implementation of the method declared in the parent class.
* @return boolean whether the flush operation was successful.
* @since 1.1.5
*/
protected function flushValues()
{
$this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName}")->execute();
return true;
}
}
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