Symfony Form builder with filtered entity association

Question

I have an form when user can book a vehicule in a period of dates.

I want to make an edit form to assign a driver to a booking car.

Now what i want is when i have to edit a booking ( id, dateFrom , dateTo , driver , vehicule ) I have a dropdown with the list of driver available in the period (datefrom , DateTo ).

I am trying to buid the form with choice type and data from query using CreateQuery Function. but it displqy nothing.

I have tried EntityType but my query to get list of available driver does not work well because the associated field (driver_id) is in the booking table not in driver table.

the schema :

Reservation (id, datedebut, datefin , vehicule , driver ... )

Driver (id , name)

Below my code:

 $em = $this->getDoctrine()->getEntityManager();
    $reservation = $em->getRepository('AppBundle:Reservation')->find($id);
            $qb = $em->createQuery("SELECT c FROM  AppBundle\Entity\Chauffeur c  left JOIN AppBundle\Entity\Reservation r 
        WITH c.id = r.vehicule
        and r.datefin >= :d1
        and r.datedebut <= :d2 where r.id IS NULL");

    $qb->setParameter('d1' , $reservation->getDatedebut() );
    $qb->setParameter('d2' , $reservation->getDatefin() );

    $chauffeurs =  $qb->getArrayResult();

    $reservation->setChauffeur($chauffeurs);

    $editForm = $this->createFormBuilder($reservation)
        ->add('client', TextType::class)
        ->add('telephone', TextType::class)
        ->add('email', TextType::class)
        ->add('datedebut', DateTimeType::class, [
            'widget' => 'single_text'])
        ->add('datefin', DateTimeType::class, [
            'widget' => 'single_text'])
        ->add('telephone', TextType::class)
        ->add('chauffeur', ChoiceType::class, array(
            'choices'   => $chauffeurs,
            'multiple'  =>  true,
            'expanded'  => true,
            ))
        ->add('modifier', SubmitType::class, array('label' => 'Modifier'))   
        ->getForm();