code: static protected function doctrine2Query(\Doctrine\ORM\EntityManager $entityManager, $entityName, $field, $generate)
      {
          $result = $entityManager->createQueryBuilder()
                                  ->select("entity.$field")
                                  ->from($entityName, 'entity')
                                  ->where("entity.$field = :$field")
                                  ->setParameter("$field", $generate)
                                  ->getQuery()
                                  ->getResult();
          
          return !empty($result);
      }
docs: Doctgrine ORM v2 generate query
  
  @param \Doctrine\ORM\EntityManager $entityManager
  @param type $entityName
  @param type $field
  @param type $generate
  @return mixed