code: def unlink(self):
          
          for reserv_rec in self:
              if reserv_rec.state != 'draft':
                  raise ValidationError(_('You cannot delete Reservation in %s\
                                           state.') % (reserv_rec.state))
          return super(HotelReservation, self).unlink()
docs: Overrides orm unlink method.
          @param self: The object pointer
          @return: True/False.