code: def unlink(self):
          
          hotel_room_reserv_line_obj = self.env['hotel.room.reservation.line']
          for reserv_rec in self:
              for rec in reserv_rec.reserve:
                  hres_arg = [('room_id', '=', rec.id),
                              ('reservation_id', '=', reserv_rec.line_id.id)]
                  myobj = hotel_room_reserv_line_obj.search(hres_arg)
                  if myobj.ids:
                      rec.write({'isroom': True, 'status': 'available'})
                      myobj.unlink()
          return super(HotelReservationLine, self).unlink()
docs: Overrides orm unlink method.
          @param self: The object pointer
          @return: True/False.