Symfony2: dynamic form using Form Events

I have some problems to make a dynamic form in my Symfony2 project. I try to follow the doc here, but it hard to understand how to really proceed with it. I try to have a form like this on the page.

Indeed, I need to create a dynamic form where dropdown list dynamically change their values when a value is selected from the dropdown list before.

This dynamic form involves 4 entities:

Parcsimmobilier.php <= ManyToOne Ensembles.php <= ManyToOne Batiments.php <= ManyToOne Zonestechnique.php

1- the first dopdown concerns the parc, when I choose a value in this dropdown, the ensembles dropdown appears. The values of the ensembles dropdown must belong to the parcs I choose first.

2- the second dropdown with ensembles value: when I selected a value, the third dropdown appears, it concerns the categories of my zones (entity Zonestechnique).

3- the zones categories dropdown have multiple choice, but when I choose the value "outside", the last dropdown with the batiments values appears but with the value "none" inevitably. But if I choose other values than "outside", the batiments dropdown appears with all batiments (belong to the ensemble I choose before).

4- when I make all this steps, the rest of the form appears (form for Zones technique entity)

I have to proceed this form when I want to add/create a new Zones technique in my database.

Here the code for my entities:

//Parcsimmobilier entity
class Parcsimmobilier
{
/**
 * @var integer
 *
 * @ORM\Column(name="id", type="integer", nullable=false)
 * @ORM\Id
 * @ORM\GeneratedValue(strategy="IDENTITY")
 */
private $id;

/**
 * @var string
 *
 * @ORM\Column(name="nom", type="string", length=150, nullable=false)
 */
private $nom;

 /**
 * @var \Doctrine\Common\Collections\Collection
 *
 * @ORM\OneToMany(targetEntity="Ensembles", mappedBy="parcsimmobilier")
 */
private $ensembles;
//end of Parcsimmobilier entity


//Ensembles entity
class Ensembles
{
/**
 * @var integer
 *
 * @ORM\Column(name="id", type="integer", nullable=false)
 * @ORM\Id
 * @ORM\GeneratedValue(strategy="IDENTITY")
 */
private $id;

 /**
 * @var string
 *
 * @ORM\Column(name="nom", type="string", length=150, nullable=false)
 */
private $nom;

 /**
 * @var \Parcsimmobilier
 *
 * @ORM\ManyToOne(targetEntity="Parcsimmobilier")
 * @ORM\JoinColumns({
 *   @ORM\JoinColumn(name="parcsimmobilier_id", referencedColumnName="id")
 * })
 */
private $parcsimmobilier;
//end of Ensembles entity


//Batiments entity
class Batiments
{
/**
 * @var integer
 *
 * @ORM\Column(name="id", type="integer", nullable=false)
 * @ORM\Id
 * @ORM\GeneratedValue(strategy="IDENTITY")
 */
private $id;

/**
 * @var string
 *
 * @ORM\Column(name="nom", type="string", length=150, nullable=true)
 */
private $nom;

/**
 * @var \Ensembles
 *
 * @ORM\ManyToOne(targetEntity="Ensembles")
 * @ORM\JoinColumns({
 *   @ORM\JoinColumn(name="ensembles_id", referencedColumnName="id")
 * })
 */
private $ensembles;
//end of Batiments entity


//Zonestechnique entity
class Zonestechnique
{
/**
 * @var integer
 *
 * @ORM\Column(name="id", type="integer", nullable=false)
 * @ORM\Id
 * @ORM\GeneratedValue(strategy="IDENTITY")
 */
private $id;

/**
 * @var string
 *
 * @ORM\Column(name="nom", type="string", length=150, nullable=false)
 */
private $nom;

/**
 * @var \Batiments
 *
 * @ORM\ManyToOne(targetEntity="Batiments")
 * @ORM\JoinColumns({
 *   @ORM\JoinColumn(name="batiments_id", referencedColumnName="id")
 * })
 */
private $batiments;

/**
 * @var \Doctrine\Common\Collections\Collection
 *
 * @ORM\ManyToMany(targetEntity="Categorieszonestechnique")
 * @ORM\JoinTable(name="zonestechnique_categorieszonestechnique",
 *   joinColumns={
 *     @ORM\JoinColumn(name="zonestechnique_id", referencedColumnName="id")
 *   },
 *   inverseJoinColumns={
 *     @ORM\JoinColumn(name="categorieszonestechnique_id", referencedColumnName="id")
 *   }
 * )
 */

 private $categorieszonestechnique;

Following the doc, this is my formtype, ZonesTechniqueType.php:

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

class ZonestechniqueType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('parcsimmobilier', 'entity', array(
                                            'class'    => 'EnexgirDatabaseBundle:Parcsimmobilier',
                                            'property' => 'nom',
                                            'multiple' => false,
                                            'required' => true,
                                            'mapped' => false,
                                            'empty_value' => '-- sélectionner un parc --',
                                            'label'    => 'Choisir le parc immobilier : ',
                                            'attr' => array('class' => 'col-xs-3 form-control')))
            ->add('nom')
            ->add('localisation')
            ->add('commentaire')
            ->add('categorieszonestechnique')
            ->add('batiments');

            $formModifier = function (FormInterface $form, Parcsimmobilier $parc = null) {
                $ensembles = null === $parc ? array() : $parc->getEnsembles();

                $form->add('ensembles', 'entity', array(
                                                'class'       => 'EnexgirDatabaseBundle:Ensembles',
                                                'property' => 'nom',
                                                'multiple' => false,
                                                'required' => true,
                                                'mapped' => true,
                                                'empty_value' => '-- sélectionner un ensemble --',
                                                'label'    => 'Choisir l\'ensemble : ',
                                                'query_builder' => function(EntityRepository $er) use ($parc) {
                                                                    return $er->createQueryBuilder('e')
                                                                        ->where("e.parcsimmobilier = :parcsimmobilier_id")
                                                                        ->orderBy('e.nom', 'ASC')
                                                                        ->setParameter(':parcsimmobilier_id', $parc);
                                                                    },
                ));
            };

            $builder->addEventListener(
                FormEvents::PRE_SET_DATA,
                function (FormEvent $event) use ($formModifier) {
                    // this would be your entity
                    $data = $event->getData();

                    $formModifier($event->getForm(), $data->getEnsembles());
                }
            );

            $builder->get('parcsimmobilier')->addEventListener(
                FormEvents::POST_SUBMIT,

This is the controller method I use for:

public function addZonesConformitesAction(Request $request) {

        $em=$this->getDoctrine()->getManager();
        $zoneConformite = $em->getRepository('EnexgirDatabaseBundle:Zonestechnique');

        $zoneConformite = new Zonestechnique;
        $form=$this->createForm(new ZonestechniqueType(), $zoneConformite);

        $form->handleRequest($request);

            //instruction if à plusieurs conditions: ici si la method est POST et si le formulaire est valide
            if ($request->isMethod('POST') | ($form->isValid())) {

                    $form->bind($request);
                    $zoneConformite = $form->getData();

                    $em->persist($zoneConformite);
                    $em->flush();

                    return $this->redirect($this->generateUrl('indexRechercheZones'));
                }

            //retourner le formulaire d'ajout si c'est invalide
            else {
                    return $this->render('EnexgirGestionEquipementsTechniquesBundle:ZonesTechnique:ajouterZonesTechniqueConformites.html.twig', array('form' => $form->createView() ));
                }
    }

And finally, the block content of my twig:

{% block content %}
    <div class="panel-heading">
      <h3 class="panel-title"> Gestion Des Zones techniques -<small>&nbsp;&nbsp;(ajout)</small></h3>
    </div>
    {# Panel Body #}
    <div class="panel-body">
      {# Menu #}
      <div class="panel-body">
        <ul class="nav nav-tabs">
            <li role="presentation">
                <a href="{{ path('indexRechercheZones') }}">Visualisation des Zones techniques</a>
            </li>
          <li role="presentation" class="active">
            <a>Ajouter une Zone technique et ses Conformités</a>
          </li>
        </ul>
      </div>
      {# Formulaire #}
      <div class="page-header">
        <h4><b><u>Ajouter une zone technique et ses conformites</u></b><small>&nbsp;&nbsp;(créer une zone technique qui n'existe pas encore, ainsi que ses conformités respectives)</small></h4>
        <br>
        <form action="{{ path('ajouterZonesConformites_process') }}" method="POST" {{ form_enctype(form) }}>
          <div>
            {{ form_start(form) }}
              {{ form_row(form.parcsimmobilier) }}    {# <select id="meetup_sport" ... #}
              {{ form_row(form.ensembles) }} {# <select id="meetup_position" ... #}
            {{ form_end(form) }}
          {# validation #}
            <input type="submit" value="Ajouter" class="btn btn-success"/>
          </div>
          <br>
        </form>
      </div>
    </div>
  {% endblock %}

For now, I have not introduce the Ajax code in my twig because I have this error:

Attempted to call method "getEnsembles" on class "Enexgir\DatabaseBundle\Entity\Zonestechnique" in C:\wamp\www\MyPathToMyProject\src\Enexgir\DatabaseBundle\Form\ZonestechniqueType.php line 65.

This is the code for the line 65:

$formModifier($event->getForm(), $data->getEnsembles());

I understand that Ensembles.php and Parcsimmobilier.php have no relation with Zonestechnique.php, but I follow the doc, and I don't really understand how this is worked. Someone could help me to understand and make this form?

Thank you in advance.