How to store MongoDB\ReferenceOne with Sonata Admin? - mongodb

Question

I have a problem Sonata Admin and storing a reference in a MongoDB document. I set up Sonata Admin correct (without reference it works well).
But if i try to store a user-reference for the cinema-document, i get the following error.
Error
Symfony\Component\Validator\ConstraintViolation
Object(Symfony\Component\Form\Form).children[user_id] = 5511710289d39769378b4567
Caused by:
Symfony\Component\Form\Exception\TransformationFailedException
Unable to reverse value for property path "user_id": The choice "5511710289d39769378b4567" does not exist or is not unique
Caused by:
Symfony\Component\Form\Exception\TransformationFailedException
The choice "5511710289d39769378b4567" does not exist or is not unique
Cinema.php
namespace Cinemato\AppBundle\Document;
use Doctrine\ODM\MongoDB\Mapping\Annotations as MongoDB;
use Cinemato\UserBundle\Document\User as User;
/**
* #MongoDB\Document
*/
class Cinema
{
/**
*
* #var integer
* #MongoDB\Id
*/
private $id;
/**
*
* #var string
* #MongoDB\String
*/
private $title;
/**
* #MongoDB\ReferenceOne(targetDocument="Cinemato\UserBundle\Document\User")
*/
private $user_id;
/**
* Get id
*
* #return id $id
*/
public function getId()
{
return $this->id;
}
/**
* Set userId
*
* #param Cinemato\AppBundle\Document\User $userId
* #return self
*/
public function setUserId(\Cinemato\AppBundle\Document\User $userId)
{
$this->user_id = $userId;
return $this;
}
/**
* Get userId
*
* #return Cinemato\AppBundle\Document\User $userId
*/
public function getUserId()
{
return $this->user_id;
}
}

Answer 1

To solve the problem the CinemaAdmin.php must be edited - sonata_type_model_list must be added in configureFormFields.
/**
* #param FormMapper $formMapper
*/
protected function configureFormFields(FormMapper $formMapper)
{
$formMapper
->add('title')
->add('user_id', 'sonata_type_model_list')
;
}