public function area(NeighborhoodBoundary $np) { $sql = "SELECT ST_Area(polygon) AS area FROM neighborhood_polygon np WHERE np.id = :np_id"; $rsm = new ResultSetMapping(); $rsm->addScalarResult('area', 'area'); $query = $this->em->createNativeQuery($sql, $rsm); $result = $query->setParameter('np_id', $np->getId())->getSingleResult(); return $result['area']; }