public Classroom getById(int id) {
   return cdao.getById(id);
 }
 public List<Classroom> getAll() {
   return cdao.getAll();
 }
 public int update(Classroom classroom) {
   return cdao.update(classroom);
 }
 public int delete(int id) {
   return cdao.delete(id);
 }
 public int insert(Classroom classroom) {
   return cdao.insert(classroom);
 }