Query for Doctrine entity that contains specified entity in a unidirectional ManyToMany relationship

TourRepository.php

<?php

namespace Acme\TourBundle\Entity;

use Doctrine\ORM\EntityRepository;
use Doctrine\ORM\NoResultException;

/**
 * TourRepository
 */
class TourRepository extends EntityRepository {
    
    /**
     * Find all tours belonging to user that do not have the provided artwork
     *
     * @param User $user
     * @param Author $author
     * @return array
     */
    public function findByUserNotContainingArtwork($user, $artwork) {
        $dql = 'SELECT t FROM AcmeTourBundle:Tour t LEFT JOIN t.user u LEFT JOIN t.artwork a WHERE u = :user AND NOT :artwork MEMBER OF t.artwork';
        $query = $this->getEntityManager()->createQuery($dql)->setParameter('user', $user)->setParameter('artwork', $artwork);
        try {
            return $query->getResult();
        }
        catch (NoResultException $e) {
            return null;
        }
    }
}