Symfony2 Many to Many relation update - php

Question

I have a many to many relation that is actually made of two many to ones on a third entity.
Domain ← one-to-many → DomainTag ← many-to-one → Tag
I'm building a Rest API, and I want to add domains to a Tag via a specific route. Everything works fine when the tags has no association.
But when I try to add new domains to a tag, there is an error if the tag already as one (or more) domain(s).
The error is
The form's view data is expected to be of type scalar, array or an instance of \ArrayAccess, but is an instance of class AppBundle\Entity\Domain. You can avoid this error by setting the "data_class" option to "AppBundle\Entity\Domain" or by adding a view transformer that transforms an instance of class AppBundle\Entity\Domain to scalar, array or an instance of \ArrayAccess.
Here are the three entities :
Tag
class Tag
{
…
/**
* #ORM\OneToMany(targetEntity="DomainTag", mappedBy="tag", cascade={"persist", "remove"})
*/
private $domainTags;
…
}
DomainTag
class DomainTag
{
…
/**
* #var Tag
*
* #ORM\ManyToOne(targetEntity="Tag", inversedBy="domainTags")
* #ORM\JoinColumns({
* #ORM\JoinColumn(name="tag_id", referencedColumnName="id")
* })
*/
private $tag;
/**
* #var Domain
*
* #ORM\ManyToOne(targetEntity="Domain", inversedBy="domainTags")
* #ORM\JoinColumns({
* #ORM\JoinColumn(name="domain_id", referencedColumnName="id")
* })
*/
private $domain;
…
}
Domain
class Domain
{
…
/**
* #ORM\OneToMany(targetEntity="DomainTag", mappedBy="domain", cascade={"persist", "remove"})
*/
private $domainTags;
…
}
Here is the form
class AddDomainTagFormType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('domainTags', 'collection', array(
'type' => new DomainTagFormType(),
'allow_add' => true,
))
;
}
// BC for SF < 2.7
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'AppBundle\Entity\Tag',
'csrf_protection' => false,
));
}
public function getName()
{
return 'api_set_domaintag';
}
}
DomainTagFormType
class DomainTagFormType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('weight')
->add('domain', 'entity', array(
'class' => 'AppBundle:Domain',
'property' => 'id',
'multiple' => false,
'expanded' => true
))
;
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'AppBundle\Entity\DomainTag',
'csrf_protection' => false,
));
}
// BC for SF < 2.7
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$this->configureOptions($resolver);
}
public function getName()
{
return 'api_domaintag';
}
}
And finally, the controller
/**
* #Rest\Put("/{id}/domains", requirements={"id" = "\d+"})
* #Security("has_role('ROLE_SUPER_ADMIN')")
* #Rest\View
*/
public function setDomainAction(Request $request, $id)
{
$tagManager = $this->get('app.manager.tag');
$domainManager = $this->get('app.manager.domain');
$tag = $tagManager->find($id);
if (!$tag) {
return new Response('Tag not found', 404);
}
$form = $this->createForm(new AddDomainTagFormType(), $tag, array('method' => 'PUT'));
$form->handleRequest($request);
if ($form->isValid()) {
foreach ($tag->getDomainTags() as $dt) {
$dt->setTag($tag);
$tagManager->persist($dt);
}
$tagManager->flush($tag);
return new Response('', 204);
} else {
return $this->view($form, 400);
}
}
Do I have to remove all DomainTags from the Tag and the recreate all associations ? Or is there a way to just add/remove DomainTags ?
Thank you