symfony : how to render edit a class json_array attribute with a list of checkboxes?

In my symfony2 application, I have an attribute of type json_array :

/**
 * @ORM\Column(name="rights", type="json_array", nullable=true)
 */
protected $rights = array();

The data for this attributeis an associative array as follows :

    $allRights = array(
        Associate::READ_PROFILE => array('all' => false),
        Associate::UPDATE_PROFILE => array('all' => false),
        Associate::READ_CONTACT => array('all', 'created' => false),
);

I want to be able to edit this attribute with a collection of checkboxes collections ie. I want one line per key of the first level and then one checkbox per key of the second level.

I have starter a form type which calls a custom type :

<?php

namespace AppBundle\Form\User;

use AppBundle\Entity\User\Associate;
use AppBundle\Form\DataTransformer\RightsToArrayTransformer;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Symfony\Component\Validator\Constraints as Assert;

class AssociateRightsType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('rights', 'fmu_rights', array(
                'label' => false,
            ));
    }

    /**
     * @param OptionsResolverInterface $resolver
     */
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'AppBundle\Entity\User\Associate',
            'validation_groups' => array('Default', 'rights'),
            'cascade_validation' => true,
        ));
    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'appbundle_user_associate_rights';
    }
}

In this custom type I have added a dataTransformer :

<?php

namespace AppBundle\Form\Type;

use AppBundle\Application\User\AssociateManager;
use AppBundle\Entity\User\Associate;
use AppBundle\Form\DataTransformer\RightsToArrayTransformer;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class RightsType extends AbstractType
{
    /**
     * @var AssociateManager
     */
    private $associateManager;

    public function __construct(AssociateManager $associateManager)
    {
        $this->associateManager = $associateManager;
    }

    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $transformer = new RightsToArrayTransformer();
        $builder->addModelTransformer($transformer);


    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'fmu_rights';
    }

}

In this data transformer I make sure the data is ouputed in the right format :

<?php

namespace AppBundle\Form\DataTransformer;

use AppBundle\Entity\User\Associate;
use Symfony\Component\Form\DataTransformerInterface;

class RightsToArrayTransformer implements DataTransformerInterface
{
    /**
     * @param mixed $data
     * @return array|mixed
     */
    public function transform($data)
    {
        return is_array($data) ? $data + $this->getRights() : $this->getRights();
    }

    /**
     * @param mixed $data
     * @return array
     */
    public function reverseTransform($data)
    {
        return $data;
    }

    private function getRights()
    {
        $allRights = array(
            Associate::READ_PROFILE => array('all'),
            Associate::UPDATE_PROFILE => array('all'),
            Associate::READ_CONTACT => array('all', 'created'),
            Associate::UPDATE_CONTACT => array('all', 'created'),
            Associate::DELETE_CONTACT => array('all', 'created'),
            Associate::IS_BOSS => array('all'),
        );

        foreach ($allRights as $right => $parameters) {
            $allRights[$right] = array();
            foreach ($parameters as $parameter) {
                $allRights[$right][$parameter] = false;
            }

        }

        return $allRights;
    }
}

and I have a custom view that makes the right visual ouput :

{% block fmu_rights_widget %}

    {% if attr.class is defined %}
        {% set attr = attr|merge({'class': attr.class ~ ' input-sm form-control fmu_rights'}) %}
    {% endif %}

    {% set rights = form.vars.data %}

    {% for right, parameters in rights %}
        <div class="row padding-v">
            <div class="col-md-2">
                {{ right }}
            </div>
            <div class="col-md-10">
                {% for parameter, value in parameters %}
                    {% set name = id ~ '[' ~ loop.index ~ ']' ~ right ~ '[' ~ parameter ~ ']' %}
                        <label for="{{ name }}">{{ parameter }}</label>
                        <input type="checkbox" id="{{ name }}" name="{{ name }}" {% if value %}checked{% endif %}>
                {% endfor %}
            </div>
        </div>
    {% endfor %}

{% endblock %}

However, the data returned when I send my form is the original data output, not the modified data. I guess I've done it wrong in the view. How can I edit this data correctly and be able to manipulate it the reverse transform function of my data transformer ?