Symfony2 UniqueEntity约束SQL错误，而不是消息

我一直在用Symfony2创建用户注册表单。我试图在User类的email属性上定义一个Unique约束。

Acme''APPBundle''Entity''User.php

namespace Acme'APPBundle'Entity;
use Doctrine'ORM'Mapping as ORM;
use Symfony'Component'Security'Core'User'UserInterface;
use Symfony'Component'Validator'Constraints as Assert;
use Symfony'Bridge'Doctrine'Validator'Constraints'UniqueEntity;
/**
* @ORM'Entity
* @ORM'Entity(repositoryClass="Acme'APPBundle'Entity'UserRepository")
* @ORM'Table("users")
* @UniqueEntity(
*       fields={"email"},
*       message="email already used"
* )
*/
class User implements UserInterface, 'Serializable
{
    /**
     * @ORM'Id
     * @ORM'Column(type="integer")
     * @ORM'GeneratedValue(strategy="AUTO")
     */
    protected $id;
    /**
     * @ORM'Column(type="string", length=255, unique=true)
     * @Assert'NotBlank()
     * @Assert'Email()
     */
    protected $email;

    [...]
}

Acme''APPBundle''Form''Type''UserType.php

namespace Acme'APPBundle'Form'Type;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilderInterface;
use Symfony'Component'OptionsResolver'OptionsResolverInterface;
class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('email', 'email');
        $builder->add('password', 'repeated', array(
            'first_name' => 'password',
            'second_name' => 'confirm',
            'type' => 'password',
        ));
    }
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'Acme'APPBundle'Entity'User',
            'cascade_validation' => true,
        ));
    }
    public function getName()
    {
        return 'user';
    }
}

我在文档后面添加了约束，但我仍然得到一个异常，比如：

An exception occured while executing 'INSERT INTO users ( ... )'
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry

看起来我在注释中定义的message值被忽略了，并且表单验证被绕过了，因为它在尝试在数据库中插入行之前应该会失败。

你能告诉我我做错了什么吗？

编辑：

根据Matteo‘Ingannatore’G.的建议，我注意到我的表格没有得到适当的验证。我忘了提到我使用了一个扩展用户表单的注册类。我已经按照Symfony Cookbook中的解释编写了代码。

因此我有：

Acme''APPBundle''Form''Model''Registration.php

namespace Acme'APPBundle'Form'Model;
use Symfony'Component'Validator'Constraints as Assert;
use Acme'APPBundle'Entity'User;
class Registration
{
    /**
     * @Assert'Type(type="Acme'APPBundle'Entity'User")
     */
    protected $user;
    /**
     * @Assert'NotBlank()
     * @Assert'True()
     */
    protected $termsAccepted;
    public function setUser(User $user)
    {
        $this->user = $user;
    }
    public function getUser()
    {
        return $this->user;
    }
    public function getTermsAccepted()
    {
        return $this->termsAccepted;
    }
    public function setTermsAccepted($termsAccepted)
    {
        $this->termsAccepted = (Boolean) $termsAccepted;
    }
}

Acme''APPBundle''Form''Type''RegistrationType.php

namespace Acme'APPBundle'Form'Type;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilderInterface;
class RegistrationType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('user', new UserType());
        $builder->add('terms', 'checkbox', array('property_path' => 'termsAccepted'));
    }
    public function getName()
    {
        return 'registration';
    }
}

Acme''APPBundle''Controller''AccountController.php

namespace Acme'APPBundle'Controller;
use Symfony'Bundle'FrameworkBundle'Controller'Controller;
use Symfony'Component'HttpFoundation'Response;
use Acme'AccountBundle'Form'Type'RegistrationType;
use Acme'AccountBundle'Form'Model'Registration;
class AccountController extends Controller
{
    public function registerAction()
    {
        $form = $this->createForm(new RegistrationType(), new Registration());
        return $this->render('AcmeAPPBundle:Account:register.html.twig', array('form' => $form->createView()));
    }

    public function createAction()
    {
        $em = $this->getDoctrine()->getEntityManager();
        $form = $this->createForm(new RegistrationType(), new Registration());
        $form->handleRequest($this->getRequest());
        if ($form->isValid()) { // FIXME !!
            $registration = $form->getData();
            $em->persist($registration->getUser());
            $em->flush();
            return $this->redirect($this->generateUrl('home'));
        }
        return $this->render('AcmeAPPBundle:Account:register.html.twig', array('form' => $form->createView()));
    }
}

我想我得到的错误可能是由于Registration表单已验证，但其中的User表单未提交验证。我错了吗？我怎么能简单地改变这种行为呢？我看到有一个cascade_validation选项，但在这里似乎没有用。我觉得奇怪的是，Symfony Cookbook提供了创建用户提供商和创建注册表的指南，但没有解释如何进行这些工作。