Doctrine2无法使用EntityManager（） - > persist保存

I am using doctrine2 in symfony 2 frame work. I am getting problem in inserting new values.My sample code is given below

$order = new Order(); 
$order->setUser($user); // $user is object from user table 
$order->setAmount($d['amount']); 
$order->setStatus($this->getStatusAsInteger($orderStatus));
$this->getEntityManager()->persist($order); 
$this->getEntityManager()->flush(); 

The code returns no error.Any one please help me to solve this issue.