Symfony嵌入表单OneToMAny editAction插入而不是更新

Question

我有OneToOne关系：用户＆lt; - ＆gt;通知：

class User implements UserInterface
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @var string
     *
     * @ORM\Column(name="username", type="string", length=50, unique=true)
     */
    protected $username;

    /**
     * @ORM\OneToOne(targetEntity="Wannity\PrivateBundle\Entity\Notification", mappedBy="user", cascade={"all"})     
     */
    protected $notifications;
}

class Notification
{
    /**
     * @ORM\Id
     * @ORM\OneToOne(targetEntity="Wannity\PublicBundle\Entity\User")
     */
    private $user;

    /**
     * @var boolean
     *
     * @ORM\Column(name="follower", type="boolean")
     */
    private $followerNotif;

class SignupCompleteType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {        
        $builder->add('email', 'email', array('attr' => array('class' => 'text')))
                ->add('notifications', new NotificationsType(), array('by_reference' => false));
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver) {
        $resolver->setDefaults(array('data_class'         => 'Wannity\PublicBundle\Entity\User',
                                     'cascade_validation' => true,));
    }

    public function getName() {
        return 'wannity_privatebundle_signupcomplete';
    }
}

class ProfileController extends Controller
{
public function configurationAction(Request $request)
    {
        $em = $this->getDoctrine()->getManager();
        $user = $this->getUser();
        $form = $this->createForm(new SignupCompleteType(), $user);
        $form->handleRequest($request);
        if($form->isValid()) {                        
            $em->persist($user);            
            $em->flush();

            return $this->redirect($this->generateUrl('home'));
        }
        return $this->render('PrivateBundle:Profile:configuration.html.twig', array(
            'form' => $form->createView()
        ));
    }
}

表单中显示了包含其值的所有字段（包括嵌入表单），但是当我提交时，Symfony尝试插入新的“通知”而不是更新现有的。为什么呢？

对不起我的英语水平。