Model transformer and expected form view data mismatch - symfony

Question

I have a Symfony 2 application, with a form that needs to store a reference to another entity (project) in a hidden field. The project entity is passed in via the form options, my plan was to have a field of the type 'hidden' that simply contains the entity id, this should then be transformed into a project entity on when the form is submitted.
I'm going about this by using a model transformer to transform between the entity to a string (it's ID). However when I try to view the form, I get the following error:
The form's view data is expected to be an instance of class Foo\BarBundle\Entity\Project, but is a(n) string. You can avoid this error by setting the "data_class" option to null or by adding a view transformer that transforms a(n) string to an instance of Foo\BarBundle\Entity\Project.
Here is my form class:
<?php
namespace Foo\BarBundle\Form\SED\Waste;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Foo\BarBundle\Form\DataTransformer\EntityToEntityIdTransformer;
/**
* Class WasteContractorEntryType
* #package Foo\BarBundle\Form\CommunityInvestment\Base
*/
class WasteContractorEntryType extends AbstractType
{
protected $name;
protected $type;
protected $phase;
protected $wasteComponent;
public function __construct($formName, $type, $phase, $wasteComponent)
{
$this->name = $formName;
$this->type = $type;
$this->phase = $phase;
$this->wasteComponent = $wasteComponent;
}
/**
* #return mixed
*/
public function getType()
{
return $this->type;
}
/**
* #return mixed
*/
public function getPhase()
{
return $this->phase;
}
/**
* #return mixed
*/
public function getProject()
{
return $this->project;
}
/**
* #return mixed
*/
public function getWasteComponent()
{
return $this->wasteComponent;
}
public function buildForm(FormBuilderInterface $builder, array $options)
{
$em = $options['em'];
$wasteComponentTransformer = new EntityToEntityIdTransformer($em,
'Foo\BarBundle\Entity\SED\Waste\WasteComponent');
$projectTransformer = new EntityToEntityIdTransformer($em, 'Foo\BarBundle\Entity\Project');
$builder->add('id', 'hidden');
$builder->add(
$builder->create('project', 'hidden', array(
'data' => $options['project'],
'by_reference' => false
))
->addModelTransformer($projectTransformer)
);
$builder->add(
$builder->create('wasteComponent', 'hidden', array(
'data' => $this->getWasteComponent()
))
->addModelTransformer($wasteComponentTransformer)
);
$builder->add('phase', 'hidden', array(
'data' => $this->getPhase()
));
$builder->add('type', 'hidden', array(
'data' => $this->getType()
));
$builder->add('percentDivertedFromLandfill', 'text', array());
$builder->add('wasteContractor', 'entity', array(
'class' => 'Foo\BazBundle\Entity\Contractor',
'property' => 'name',
'attr' => array(
'class' => 'js-select2'
)
));
}
public function getName()
{
return $this->name;
}
/**
* {#inheritDoc}
*/
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$resolver->setDefaults(array(
'csrf_protection' => true,
'data_class' => 'Foo\BarBundle\Entity\SED\Waste\WasteContractorEntry'
))
->setRequired(array(
'em',
'project'
))
->setAllowedTypes(array(
'em' => 'Doctrine\Common\Persistence\ObjectManager',
'project' => 'Foo\BarBundle\Entity\Project'
));
}
}
And my model transformer class:
<?php
namespace Foo\BarBundle\Form\DataTransformer;
use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\TransformationFailedException;
use Doctrine\Common\Persistence\ObjectManager;
class EntityToEntityIdTransformer implements DataTransformerInterface
{
/**
* #var ObjectManager
*/
private $om;
/**
* #var Entity class
*/
protected $entityClass;
/**
* #param ObjectManager $om
*/
public function __construct(ObjectManager $om, $className)
{
$this->om = $om;
$this->entityClass = $className;
}
protected function getEntityClass()
{
return $this->entityClass;
}
/**
* Transforms an object (project) to a string (id).
*
* #param Project|null $issue
* #return string
*/
public function transform($entity)
{
if (null === $entity) {
return "";
}
return $entity->getId();
}
/**
* Transforms a string (id) to an object (project).
*
* #param string $id
*
* #return Issue|null
*
* #throws TransformationFailedException if object (project) is not found.
*/
public function reverseTransform($id)
{
if (!$id) {
return null;
}
$entity = $this->om
->getRepository($this->getEntityClass())
->find($id);
if (null === $entity) {
throw new TransformationFailedException(sprintf(
'An entity of class %s with id "%s" does not exist!',
$this->getEntityClass(),
$id
));
}
return $entity;
}
}
I've tried using a adding the transformer as a view transformer instead of a model transformer, however then I just get a slightly different error:
The form's view data is expected to be an instance of class
Foo\BarBundle\Entity\Project, but is a(n) integer. You can avoid this
error by setting the "data_class" option to null or by adding a view
transformer that transforms a(n) integer to an instance of
Foo\BarBundle\Entity\Project.

Answer 1

It seems that setting 'data_class' to null as suggested by the exception message above is the solution. I had previously rejected this as it seems counter-intuitive when we know that the purpose of the field is to reference a project entity.
With the 'data_class' option set to null, the hidden project field contains the project id, and upon submission, calling getProject() on the created entity returns the correct project object.