Symfony form querybuilder with parameters

->add( 'weeks', 'entity', array(
    'class' => 'MV\CaravanBundle\Entity\CaravanRow',
    'property' => 'line',
    'query_builder' => function(EntityRepository $er ) use ( $caravan ) {
        return $er->createQueryBuilder('w')
                  ->orderBy('w.dateFrom', 'ASC')
                  ->where('w.caravan = ?1')
                  ->andWhere('w.visible = 1')
                  ->andWhere('w.booked = 0')
                  ->setParameter(1, $caravan);
}

Source: http://stackoverflow.com/a/13847387