public function findByAbbrevation($abbrevation, $returnAsEntity = false)
    {
        try {
            $qb = $this->createQueryBuilder('unit')
                ->select('partial unit.{id}')
                ->join('unit.mappings', 'mappings', 'WITH', 'mappings.name = :abbrevation')
                ->setParameter('abbrevation', $abbrevation);

            if ($returnAsEntity) {
                return $qb->getQuery()->getSingleResult();
            }

            return $qb->getQuery()->getSingleScalarResult();
        } catch (NoResultException $exc) {
            return null;
        }
    }