Difference between #2 and #1 of How to use nested DB transactions (MySQL 5+, PostgreSQL)

db, mysql, postgresql

source code taken from: [PHP, PDO & Nested
Transactions](http://www.kennynet.co.uk/2008/12/02/php-pdo-nested-transactions/)

tested with: MySql 5.1.30

Problem:
Say there is service layer in an application, and one service may use others. No
each service deals will complex business logic will needs to wrap that into
transactions.

If there are services A and B here's how it might happen:

    class~~~
[php]
class ServiceA {
        public
    public function transA() {
            $trans
        $trans = Yii::app()->db->beginTransaction();
            //
        // code
            Yii::app()->serviceB->transB();
            //
        Yii::app()->serviceB->transB();
        // code
            //
        // exception handling and stuff
            $trans->commit();
        }
        $trans->commit();
    }
    
    class}

class ServiceB {
        public
    public function transB() {
            $trans
        $trans = Yii::app()->db->beginTransaction();
            //
        // code
            //
        // exception handling and stuff
            $trans->commit();
        }
        $trans->commit();
    }
}
~~~

With default Yii implementation, PDO will throw exception saying there already
is active transaction.

But there's a solution:)

First, you'll need to extend PDO class:

	class~~~
[php]
class InsPDO extends PDO {
	    //
    // Database drivers that support SAVEPOINTs.
	    protected
    protected static $savepointTransactions = array("pgsql",
"mysql");
	
	    // The current transaction level.
	    protected $transLevel = 0;
	
	    protected function nestable() {
	        return in_array($this->getAttribute(PDO::ATTR_DRIVER_NAME),
	                        self::$savepointTransactions);
	    }
	
	    public function beginTransaction() {
	        if(!$this->nestable() || $this->transLevel == 0) {
	            parent::beginTransaction();
	        } else {
	            $this->exec("SAVEPOINT LEVEL{$this->transLevel}");
	        }
	
	        $this->transLevel++;
	    }
	
	    public function commit() {
	        $this->transLevel--;
	
	        if(!$this->nestable() || $this->transLevel == 0) {
	            parent::commit();
	        } else {
	            $this->exec("RELEASE SAVEPOINT
LEVEL{$this->transLevel}");
	        }
	    }
	
	    public function rollBack() {
	        $this->transLevel--;
	
	        if(!$this->nestable() || $this->transLevel == 0) {
	            parent::rollBack();
	        } else {
	            $this->exec("ROLLBACK TO SAVEPOINT
LEVEL{$this->transLevel}");
	        }
	    }
	}

Then, you'll need to alter CDbConnection::createPdoInstance. There, change
$pdoClass to your class name (InsPDO in this example).    // The
current transaction level.
    protected $transLevel = 0;

	protected    protected function createPdoInstance()
	{
		$pdoClass='InsPDO';
		if(($pos=strpos($this->connectionString,':'))!==false)
		{
			$driver=strtolower(substr($this->connectionString,0,$pos));
			if($driver==='mssql' || $driver==='dblib')
				$pdoClass='CMssqlPdoAdapter';
		}
		return new $pdoClass($this->connectionString,$this->username,
									$this->password,$this->_attributes);
	}nestable() {
        return in_array($this->getAttribute(PDO::ATTR_DRIVER_NAME),
                        self::$savepointTransactions);
    }

It'd probably be better OOP to extend CDbConnection, especially since
createPdoInstance is protected. But then either there are inconsistencies with
private/protected properties of CDbConnection, or I didn't spent enough time to
explore how to properly extend CDbConnection.    public function
beginTransaction() {
        if(!$this->nestable() || $this->transLevel == 0) {
            parent::beginTransaction();
        } else {
            $this->exec("SAVEPOINT LEVEL{$this->transLevel}");
        }

That's it, there you go;)        $this->transLevel++;
    }

    public function commit() {
        $this->transLevel--;

        if(!$this->nestable() || $this->transLevel == 0) {
            parent::commit();
        } else {
            $this->exec("RELEASE SAVEPOINT
LEVEL{$this->transLevel}");
        }
    }

    public function rollBack() {
        $this->transLevel--;

        if(!$this->nestable() || $this->transLevel == 0) {
            parent::rollBack();
        } else {
            $this->exec("ROLLBACK TO SAVEPOINT
LEVEL{$this->transLevel}");
        }
    }
}
~~~

Then, you'll need to alter [CDbConnection::createPdoInstance()]. There, change
$pdoClass to your class name (InsPDO in this example).

~~~
[php]
protected function createPdoInstance()
{
    $pdoClass='InsPDO';
    if(($pos=strpos($this->connectionString,':'))!==false)
    {
        $driver=strtolower(substr($this->connectionString,0,$pos));
        if($driver==='mssql' || $driver==='dblib')
            $pdoClass='CMssqlPdoAdapter';
    }
    return new $pdoClass($this->connectionString,$this->username,
                                $this->password,$this->_attributes);
}
~~~

It'd probably be better OOP to extend [CDbConnection], especially since
createPdoInstance is protected. But then either there are inconsistencies with
private/protected properties of [CDbConnection], or I didn't spent enough time
to explore how to properly extend [CDbConnection].

That's it, there you go;)