The method failTrans() forces a roll back of a smart transaction. The method can be called anywhere inside a transaction scope, but the rollback actually occurs at the point where completeTrans() is invoked.

/*
 * Assume database connection
 */
$db->startTrans();
 
/*
 * some reason to rollback transaction
 */
 
$db->failTrans();
 
/*
* Lots more code inside the transaction scope
*/
 
$db->completeTrans(); //<---- at this point, the rollback is invoked