How to use nested DB transactions (MySqlQL 5+, PgSqlostgreSQL)

TutorialHow-tos

sSource code taken from: [PHP, PDO & Nested Transactions](http://www.kennynet.co.uk/2008/12/02/php-pdo-nested-transactions/). tTested with: MySqlQL 5.1.30 + Yii 1.1.8.

Problem: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 and save it in your the protected/components directory:```

Then, you'll need to alter the behaviour of [CDbConnection::createPdoInstance()]. You can do this by making a subclass of it in protected/components/NestedDbConnection.php
 
 
There, change $pdoClass toNow your class name (NestedPDO in this example):
 
 
```php 
class NestedDbConnection extends CDbConnection
 
{
 
    protected function createPdoInstance()
 
    {
 
        $pdoClass='NestedPdo';
 
        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);
 
    }
 
}
 
```
 
 
Note that $this->_attributes was also changed to $this->attributes so the subclassing will work.
 
 
Now you can add the class name to thean use it in db configuration array in `protected/config/main.php`: ```php 'db'=>array(        'c'pdoClass' => 'NestedDbConnection',
 
       PDO',
 
'connectionString' => ...         ), ``` That's it, there you go ;)