public List <SellingBills> LoadSellingBillsByCustomerPhone(string customerphone)
        {
            List <SellingBills> sellingBillsList = new List <SellingBills>();

            DataTable data = DataProvider.Instance.ExecuteQuery("SELECT * FROM SellingBills WHERE CUSTOMERPHONE = N'" + customerphone + "'");

            foreach (DataRow item in data.Rows)
            {
                SellingBills orderbills = new SellingBills(item);
                sellingBillsList.Add(orderbills);
            }

            return(sellingBillsList);
        }
        // Xuất danh sách SellingBills
        public List <SellingBills> LoadSellingBills()
        {
            List <SellingBills> sellingBillsList = new List <SellingBills>();

            DataTable data = DataProvider.Instance.ExecuteQuery("SELECT * FROM SellingBills");

            foreach (DataRow item in data.Rows)
            {
                SellingBills orderbills = new SellingBills(item);
                sellingBillsList.Add(orderbills);
            }

            return(sellingBillsList);
        }