具有多个数据库的symfony2查询构建器（doctrine）

Question

I want join the abteilung table which is in another database with other access data.

Here is the right database for abteilung:

$manager = $this->getDoctrine()->getManager('olddb')->getRepository('ChrisOldUserBundle:BpDepartment');

And this is the old query i want to change:

$result = $this->getDoctrine()->getRepository('KfzBuchungBundle:Rent')
                ->createQueryBuilder('r')
                ->addSelect('abteilung')
                ->addSelect('auto')
                ->join('r.auto','auto')
                ->join('r.abteilung','abteilung')
                ->where('r.mieteStart >= :date_from')
                ->andWhere('r.mieteEnde <= :date_to')
                ->setParameter('date_from', $date_from)
                ->setParameter('date_to', $date_to)
                ->orderBy('r.mieteStart', 'ASC')
                ->distinct()
                ->getQuery()->getArrayResult();

I tried with:

$rsm = new ResultSetMapping();
            $rsm->addEntityResult('Chris\KfzBuchungBundle\Entity\Rent', 'bp');
            $rsm->addEntityResult('Chris\Bundle\OldUserBundle\Entity\BpDepartment', 'bp_dpt');
            $rsm->addFieldResult('bp','id','id');
            $query = $this->getDoctrine()->getManager()->createNativeQuery('SELECT * FROM bp_department bp_dpt', $rsm);

            $result = $query->getResult();

But same shit, i have no idea.