I want to get a room rate and the price of services used to make payment, then I must do so.
code:

class guest_room(models.Model):
    _name = 'guest'

    name = fields.Char(string="Họ tên", required=True, size=50)
    cmnd = fields.Integer(string="Số CMND", required=True, size=12)
    sdt = fields.Integer(string="SĐT", required=True, size=10)
    time_in = fields.Datetime(string="Ngày đến")
    time_out = fields.Datetime(string="Ngày trả")
    description = fields.Html("Ghi chú", size=1000)
    # servicesd = fields.Many2one('service', string="Dịch vụ sử dụng")
    servicesd_ids = fields.One2many('room.line', 'line', 'Dịch vụ')
    roomsd = fields.Many2one('room', string="Phòng thuê")


class RoomLine(models.Model):
    _name = 'room.line'

    line = fields.Many2one('guest')
    name = fields.Many2one('service', 'Dịch vụ')

and bills
class Bill(models.Model):
    _name = 'bills'

    kh_thue = fields.Many2one('guest', 'Khách hàng')
    total = fields.Integer(compute="_get_total", string='Tổng')

    @api.multi
    @api.depends("kh_thue")
    def _get_total(self):
        if kh_thue != None:
            total = kh_thue.roomsd.price + kh_thue.servicesd_ids.price_service