Entity Field type hidden in Symfony2 - symfony

Question

I want to make a hidden value for my Foreign Key Entity in controller.
My previous controller is like this (works fine):
->add('id_grup', 'entity', array('class' => 'Sifo\AdminBundle\Entity\MstGrup'))
I want to assign a hidden value to my form like this:
->add('id_grup', 'hidden', array('data' => $id))
But it gives me an error:
ContextErrorException: Catchable Fatal Error: Argument 1 passed to
Sifo\AdminBundle\Entity\DftGrupMapel::setIdGrup() must be an instance
of Sifo\AdminBundle\Entity\MstGrup, string given, called in
C:\Sifony\vendor\symfony\symfony\src\Symfony\Component\PropertyAccess\PropertyAccessor.php
on line 360 and defined in
C:\Sifony\src\Sifo\AdminBundle\Entity\DftGrupMapel.php line 179
How can I assign a value to a foreign key entity which is hidden?

Answer 1

Finally it works! I need define the entity default before create form and don't add again in FormBuilder:
public function manageAction(Request $request, $id)
{
$em = $this->getDoctrine()->getManager();
$entity = $em->getRepository('SifoAdminBundle:MstGrup')->find($id);
if (!$entity) {
throw $this->createNotFoundException('Unable to find MstGrup entity.');
}
$entity_new = new DftGrupMapel();
$entity_new->setIdGrup($entity);
$new_form = $this->createFormBuilder($entity_new)
->setAction($this->generateUrl('admin_grup_mapel_manage', array('id' => $id)))
->setMethod('POST')
->getForm();
$new_form->handleRequest($request);
if ($new_form->isValid()) {
$em_new = $this->getDoctrine()->getManager();
$em_new->persist($entity_new);
$em_new->flush();
return $this->redirect($this->generateUrl('admin_grup_mapel_manage', array('id' => $id)));
}
return $this->render('SifoAdminBundle:DftGrupMapel:manage.html.twig', array(
'entity' => $entity,
'new_form' => $new_form->createView(),
));
}