如何在 Doctrine 2 中使用 QueryBuilder 创建带有 SELECT 子查询的 LEFT JOIN?

I need to limit LEFT JOIN results, so I must use subquery. Could somebody give me advice how can I do it with Doctrine 2?

我现在拥有的是:

  $qb = $this->_em->createQueryBuilder();
    return $qb->add('select', 'c,j')
             ->add('from', 'JobeetBundle:Category c')
             ->leftJoin('c.jobs', 'j', 'WITH', 'j.category = c')
             ->add('where', 'j.expiresAt > ?1')
             ->add('orderBy','j.expiresAt DESC')
             ->setParameter(1, new DateTime())
             ->getQuery()
             ->getResult();

但我必须更改它以将每个类别的工作结果限制为 10 个.