Symfony2 form widget mixed between entity & choice

DoctrineChoiceType.php

<?php

namespace Acme\DemoBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Doctrine\Bundle\DoctrineBundle\Registry;
use Symfony\Component\OptionsResolver\Options;
use Doctrine\Common\Util\Inflector;
use Symfony\Component\Form\Exception\FormException;

/**
 * DoctrineChoiceType est le chainon manquant entre le type choice et le type entity
 * 
 * permet de faire une liste de choix clé => valeur depuis une table
 *
 * @author David Epely <[email protected]>
 */
class DoctrineChoiceType extends AbstractType
{
    protected $registry;
    
    public function __construct(Registry $registry) 
    {
        $this->registry = $registry;
    }
    
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $registry = $this->registry;
        //closure qui sera passé au widget parent pour définir les choix
        $choices = function(Options $options) use ($registry) {
            
            if (!isset($options['class']) || empty($options['class'])) {
                throw new FormException('class must be defined');
            }

            if (!isset($options['property']) || empty($options['property'])) {
                throw new FormException('property must be defined');
            }

            //repository de la classe à lister
            $repository = $registry->getRepository($options['class']);
            
            $property = Inflector::classify($options['property']);
            $propertyValue = ($options['property_value']) ? $options['property_value'] : $property;
            
            //résultats de la requete : tableau d'entités
            if ($options['query_builder']) {
                $results = $options['query_builder']($repository)
                        ->getQuery()
                        ->execute();
            } else {
                //par défaut on liste tout
                $results = $repository->findAll();
            }
            
            
            //géneration d'un tableau simple clé => valeur fournit au widget parent : choice
            $choices = array();
            
            array_map(function($entity) use ($property, $propertyValue, &$choices) {
                $choices[$entity->{'get' . $propertyValue}()] = 
                        $entity->{'get' . $property}();
            }, $results);
            
            return $choices;
        };
        
        $resolver->setDefaults(array(
            'class' => null,
            'choices' => $choices,
            'property' => null,
            'property_value' => null,
            'query_builder' => null,
        ));
    }

    public function getParent()
    {
        return 'choice';
    }

    public function getName()
    {
        return 'doctrineChoice';
    }
}

service.yml

services:
    
    acme.form.type.doctrine_choice:
        class: Acme\DemoBundle\Form\Type\DoctrineChoiceType
        arguments: [@doctrine]
        tags: [{name: form.type, alias: doctrineChoice}]