How to use CollectionType with FosRestBundle

Question

I'm building an API with the FOSRestBundle and I'm trying to add existing Employee entities to an existing Report entity. But my form validation keeps throwing an error: This form should not contain extra fields

Adding 'allow_add' => true to the ReportType options is not an option because I only want to add excisting employees to the Report. How can I make this work?

PUT request body

{  
    "report":{  
        "notes":"This is a note.",
        "client":5,
        "contactPerson":4,
        "contributors":[
            {
                "id": 10
            }
        ]
   }
}

ReportType

class ReportType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('notes')
            ->add('client', 'entity', array(
               'class' => 'ApiBundle:Client'
            ))
            ->add('contactPerson', 'entity', array(
               'class' => 'ApiBundle:ContactPerson'
            ))
            ->add('contributors', CollectionType::class, array(
                'entry_type'   => EmployeeType::class,
                'by_reference' => false
            ))
        ;
    }

    /**
     * @param OptionsResolver $resolver
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'ApiBundle\Entity\Report',
            'csrf_protection' => false,
            'allow_extra_fields' => true
        ));
    }
}

Snippet from Report entity

/**
 * @ORM\ManyToMany(targetEntity="ApiBundle\Entity\Employee", inversedBy="contributions", cascade={"persist"})
 * @ORM\JoinTable(name="reports_contributors")
 */
private $contributors;

/**
 * Constructor
 */
public function __construct()
{
    $this->contributors = new \Doctrine\Common\Collections\ArrayCollection();
}

/**
 * Add contributor
 *
 * @param \ApiBundle\Entity\Employee $contributor
 *
 * @return Report
 */
public function addContributor(\ApiBundle\Entity\Employee $contributor)
{
    $this->contributors[] = $contributor;

    return $this;
}

/**
 * Remove contributor
 *
 * @param \ApiBundle\Entity\Employee $contributor
 */
public function removeContributor(\ApiBundle\Entity\Employee $contributor)
{
    $this->contributors->removeElement($contributor);
}

/**
 * Get contributors
 *
 * @return \Doctrine\Common\Collections\Collection
 */
public function getContributors()
{
    return $this->contributors;
}

Snippet from Employee Entity

/**
 * @ORM\ManyToMany(targetEntity="ApiBundle\Entity\Report", mappedBy="contributors")
 */
private $contributions;

public function __construct() {
    $this->contributions = new \Doctrine\Common\Collections\ArrayCollection();
}

/**
 * Add contribution
 *
 * @param \ApiBundle\Entity\Report $contribution
 *
 * @return Employee
 */
public function addContribution(\ApiBundle\Entity\Report $contribution)
{
    $this->contributions[] = $contribution;

    return $this;
}

/**
 * Remove contribution
 *
 * @param \ApiBundle\Entity\Report $contribution
 */
public function removeContribution(\ApiBundle\Entity\Report $contribution)
{
    $this->contributions->removeElement($contribution);
}

/**
 * Get contributions
 *
 * @return \Doctrine\Common\Collections\Collection
 */
public function getContributions()
{
    return $this->contributions;
}

Solved it!

No need to use CollectionType. The solution is to use an EntityType with the multiple option.

->add('contributors', 'entity', array(
    'class' => 'ApiBundle:Employee',
    'multiple' => true
))

PUT request body

{  
   "report":{  
        "notes":"This is a note.",
        "client":5,
        "contactPerson":4,
        "contributors":[10,6]
   }
}