[doctrine2] quering entities with STI (Single table inheritance) pattern

gistfile1.aw

<?php

/** @ORM\Table(name="file")
 * @ORM\InheritanceType("SINGLE_TABLE")
 * @ORM\DiscriminatorColumn(name="function", type="smallint")
 * @ORM\DiscriminatorMap({
 *   "1" = "\..\File\CvFile",
 *   "2" = "\..\File\CvWebFile",
 *   "3" = "\..\File\KbisFile"
 * })
 */
class File extends BaseFile
{
  // ..
}

// let's say we have relation member mant-to-many file
// how to select only CvWebFile???

class MemberFileRepository extends EntityRepository
{
    public function findOneCvWebByMember(Member $member)
    {
        $q = $this->createQueryBuilder('mf')
            ->join('mf.file', 'f')
            ->where('mf.member = :member')
            ->andWhere('f INSTANCE OF \..\File\CvWebFile')
            ->setParameter('member', $member)
            ->getQuery();

        return $q->getOneOrNullResult();
    }
}