title: Symfony2 insert form value after bind() and before check isValid()
body: <p>I want the combination of both fbid and game_id be unique.
  I want to test it with the form->isValid() method. But I don't want to pass this values by hidden input.</p>
  
  <p>My entity code:</p>
  
  <pre><code>/**
   * @ORM\Entity
   * @ORM\Table(name="Member",
   *     uniqueConstraints={
   *         @ORM\UniqueConstraint(columns={"fbid", "game_id"})
   *          })
   * @UniqueEntity(fields={"fbid","game"})
   */
  class Member
  {
      /**
       * @ORM\Id
       * @ORM\Column(type="integer")
       * @ORM\GeneratedValue(strategy="AUTO")
       */
      protected $id;
  
      /**
       * @ORM\ManyToOne(targetEntity="Game", inversedBy="members")
       * @ORM\JoinColumn(name="game_id", referencedColumnName="id")
       */
      protected $game;
  
      /**
       * @ORM\Column(type="string")
       */
      private $fbid;
  </code></pre>
  
  <p>I try:</p>
  
  <pre><code>if ($request-&gt;getMethod() == 'POST') {
      $form-&gt;bind($request);
      $member = $form-&gt;getData();
      $member-&gt;setGame( $this-&gt;game );
      $form-&gt;setData($member);
      if ($form-&gt;isValid()) {
  </code></pre>
  
  <p>But I have this problem:</p>
  
  <blockquote>
    <p>You cannot change the data of a bound form</p>
  </blockquote>