title: Symfony2 Form FormType Itself collection
body: <p>I'm trying to create a symfony 2 form 'PersonType', which has a <code>PersonType</code> collection field that should map a given person's children.</p>
  
  <p>And I'm getting this error,</p>
  
  <pre><code>{"message":"unable to save order","code":400,"errors":["This form should not contain extra fields."]}
  </code></pre>
  
  <p>Here is my <code>Person</code> entity,</p>
  
  <pre><code>class Person
  {
      private $id;
  
      /**
       * @ORM\OneToMany(targetEntity="Person", mappedBy="parent", cascade={"persist"})
       */
      private $children;
  
      /**
       * @ORM\ManyToOne(targetEntity="Person", inversedBy="children")
       * @ORM\JoinColumn(name="orderitem_id", referencedColumnName="id", nullable=true)
       */
      private $parent;
  
  }
  </code></pre>
  
  <p>And my Type,</p>
  
  <pre><code>class PersonType extends AbstractType
  {
      /**
       * @param FormBuilderInterface $builder
       * @param array $options
       */
      public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder
              -&gt;add('id')
              -&gt;add('children', 'collection', array(
                  'type' =&gt; new PersonType()
              ))
          ;
      }
  </code></pre>
  
  <p>UPDATE :
   I've seen that the problem was because the option :</p>
  
  <pre><code>'allow_add' =&gt; true,
  'by_reference' =&gt; false
  </code></pre>
  
  <p>wasn't in the Type, I've deleted it because when i insert them, the form don't appear and the page crash with no error.</p>
  
  <p>I'm very confused because with this error, people can't have children :/</p>
  
  <p>Does anyone already faced the same problem? (A formType nested over itself)</p>
  
  <p>ACUTALLY :
  I've duplicate my personType to PersonchildrenType to insert this last in the first...</p>