title: uniqueEntity multiple fields
body: <p>I have two unique attributes in my entity :</p>
  
  <pre><code>/**
   * @ORM\Column(type="string", length=100, unique=true, nullable=true)
   */
  private $username;
  
  /**
   * @ORM\Column(type="string", length=80, unique=true)
   * @Assert\Email()
   */
  private $email;
  </code></pre>
  
  <p>I have add the uniqueentity annotation at the first of the class:</p>
  
  <pre><code>/**
   * @ORM\Entity
   * @UniqueEntity(fields = {"username"}, message="This user already exits")
   * @UniqueEntity(fields = {"email"}, message="This email already exists")
   */
  class User
  </code></pre>
  
  <p>But the email field is good tested and detect if I have already the same email in database, but the username not.</p>
  
  <p>What I'm doing wrong?</p>
  
  <p>Thanks</p>
  
  <p>Best regards</p>
  
  <p>EDIT:</p>
  
  <pre><code> public function buildForm(FormBuilderInterface $builder, array $options) {
          $builder
                  -&gt;add('email', 'text', array('label' =&gt; 'form.label.email', 'attr' =&gt; array('placeholder' =&gt; 'form.placeholder.email')))
                  -&gt;add('username', 'text', array('label' =&gt; 'form.label.username', 'attr' =&gt; array('placeholder' =&gt; 'form.placeholder.username')))
  ...
  
  -&gt;add('envoyer', 'submit', array('label' =&gt; 'form.submit', 'attr' =&gt; array('class' =&gt; 'col-lg-12 col-xs-12 btn btn-primary submit')))
              ;
  </code></pre>