Edit form returns null value Symfony2 - symfony

Question

I have an Edit Form in my application and when tries to save (insert) the new record I get this error message:
An exception occurred while executing 'INSERT INTO in_orden_compra_detalle (id_orden_compra, id_producto, cantidad, precio_compra, total, entrega, fecha_entrega) VALUES (?, ?, ?, ?, ?, ?, ?)' with params [null, null, 89, 45, null, null, null]:
Table in_orden_compra_detalle is related to 2 tables (in_producto and in_orden_compra)
Here my relatioship:
class InOrdenCompra
{
/**
* #ORM\ManyToOne(targetEntity="InProveedor", inversedBy="InOrdenCompra")
* #ORM\JoinColumn(name="id_proveedor", referencedColumnName="id")
*/
protected $proveedorOc;
/**
* #ORM\ManyToOne(targetEntity="Nival\AccesoBundle\Entity\AdUsuario", inversedBy="InOrdenCompra")
* #ORM\JoinColumn(name="id_usuario", referencedColumnName="id_usuario")
*/
/**
* #ORM\OneToMany(targetEntity="InOrdenCompraDetalle", mappedBy="InOrdenCompra", cascade={"persist"})
*/
protected $ordenCompra;
class InProducto
{
/**
* #ORM\OneToMany(targetEntity="InOrdenCompraDetalle", mappedBy="InProducto", cascade={"persist"})
*/
protected $productoOc;
public function __construct()
{
$this->productoOc = new ArrayCollection();
}
public function __toString() {
return $this->nombre;
}
class InOrdenCompraDetalle
{
/**
* #ORM\ManyToOne(targetEntity="InOrdenCompra", inversedBy="InOrdenCompraDetalle")
* #ORM\JoinColumn(name="id_orden_compra", referencedColumnName="id")
*/
protected $ordenCompra;
/**
* #ORM\ManyToOne(targetEntity="InProducto", inversedBy="InOrdenCompraDetalle")
* #ORM\JoinColumn(name="id_producto", referencedColumnName="id_producto")
*/
protected $productoOc;
My Controller for new record:
public function newAction($id_orden_compra)
{
$entity = new InOrdenCompraDetalle();
$entity->setOrdenCompra($this->get('doctrine')->getRepository('NivalInventarioBundle:InOrdenCompra')->find($id_orden_compra));
$form = $this->createCreateForm($entity, $id_orden_compra);
return $this->render('NivalInventarioBundle:InOrdenCompraDetalle:new.html.twig', array(
'id_orden_compra' => $id_orden_compra,
'entity' => $entity,
'form' => $form->createView(),
));
}
I need to pass the id_orden_compra value to setOrdenCompra in entity InOrdenCompraDetalle.
Also id_producto should have the value selected from entity field:
->add('productoOc', 'entity', array(
'class' => 'NivalInventarioBundle:InProducto',
'query_builder' => function (EntityRepository $er) {
return $er->createQueryBuilder('u')
->orderBy('u.nombre', 'ASC');
},
'choice_label' => function ($displayname) {
return $displayname->getDisplayName();},
'by_reference' => true,
'expanded' => false,
'placeholder' => 'Seleccione una opción',
'mapped' => true,
'multiple' => false,
))
->add('cantidad')
->add('precioCompra')
But also comes null.
Please help
UPDATED
public function createAction(Request $request, $id_orden_compra)
{
$entity = new InOrdenCompraDetalle();
$form = $this->createCreateForm($entity, $id_orden_compra);
$form->handleRequest($request);
if ($form->isValid()) {
$em = $this->getDoctrine()->getManager();
$em->persist($entity);
$em->flush();
return $this->redirect($this->generateUrl('inordencompradetalle_show', array('id_orden_compra' => $id_orden_compra, 'id' => $entity->getId())));
}
return $this->render('NivalInventarioBundle:InOrdenCompraDetalle:new.html.twig', array(
'id_orden_compra' => $id_orden_compra,
'entity' => $entity,
'form' => $form->createView(),
));
}
createCreateForm:
private function createCreateForm(InOrdenCompraDetalle $entity, $id_orden_compra)
{
$form = $this->createForm(new InOrdenCompraDetalleType(), $entity, array(
'action' => $this->generateUrl('inordencompradetalle_create', array('id_orden_compra' => $id_orden_compra)),
'method' => 'POST',
));
return $form;
}