Symfony2 doctrine select IFNULL

Хорошо, у меня есть этот код:

SELECT 
IFNULL(s2.id,s1.id) AS effectiveID, 
IFNULL(s2.status, s1.status) AS effectiveStatus, 
IFNULL(s2.user_id, s1.user_id) as effectiveUser,
IFNULL(s2.likes_count, s1.likes_count) as effectiveLikesCount

FROM statuses AS s1
LEFT JOIN statuses AS s2 ON s2.id = s1.shared_from_id
WHERE s1.user_id = 4310
ORDER BY effectiveID DESC
LIMIT 15

И мне нужно переписать его в querybuilder. Что-то вроде этого?

        $fields = array('IFNULL(s2.id,s1.id) AS effectiveID','IFNULL(s2.status, s1.status) AS effectiveStatus', 'IFNULL(s2.user_id, s1.user_id) as effectiveUser','IFNULL(s2.likes_count, s1.likes_count) as effectiveLikesCount');

    $qb=$this->_em->createQueryBuilder()
             ->select($fields)
             ->from('WallBundle:Status','s1')
             ->addSelect('u')
             ->where('s1.user = :user')
             ->andWhere('s1.admin_status = false')
             ->andWhere('s1.typ_statusu != :group')
             ->setParameter('user', $user)
             ->setParameter('group', 'group')
             ->leftJoin('WallBundle:Status','s2', 'WITH', 's2.id=s1.shared_from_id')  
             ->innerJoin('s1.user', 'u')               
             ->orderBy('s1.time', 'DESC')
             ->setMaxResults(15);

     var_dump($query=$qb->getQuery()->getResult());die();

Эта ошибка

[Syntax Error] line 0, col 7: Error: Expected known function, got 'IFNULL'