code: def cancel_reservation(self):
          
          room_res_line_obj = self.env['hotel.room.reservation.line']
          hotel_res_line_obj = self.env['hotel_reservation.line']
          self.state = 'cancel'
          room_reservation_line = room_res_line_obj.search([('reservation_id',
                                                             'in', self.ids)])
          room_reservation_line.write({'state': 'unassigned'})
          room_reservation_line.unlink()
          reservation_lines = hotel_res_line_obj.search([('line_id',
                                                          'in', self.ids)])
          for reservation_line in reservation_lines:
              reservation_line.reserve.write({'isroom': True,
                                              'status': 'available'})
          return True
docs: This method cancel record set for hotel room reservation line
          ------------------------------------------------------------------
          @param self: The object pointer
          @return: cancel record set for hotel room reservation line.