Get random table row with doctrine DQL in Symfony2

gistfile1.php

<?php
// 
// Theory (for MySQL): http://jan.kneschke.de/projects/mysql/order-by-rand/
//

class QuestionRepository extends EntityRepository
{
    public function findOneRandom()
    {
        $em = $this->getEntityManager();
        $max = $em->createQuery('
            SELECT MAX(q.id) FROM EnzimQuestionBundle:Question q
            ')
            ->getSingleScalarResult();
        return $em->createQuery('
            SELECT q FROM EnzimQuestionBundle:Question q 
            WHERE q.id >= :rand
            ORDER BY q.id ASC
            ')
            ->setParameter('rand',rand(0,$max))
            ->setMaxResults(1)
            ->getSingleResult();
    }
}