public bool insert(DTO_PhieuDatHang obj)
        {
            using (CellphoneComponentEntities db = new CellphoneComponentEntities())
            {
                var resultMaNhanVien = db.Database
                                       .SqlQuery <String>("select MaNhanVien from dbo.NhanVien where TenNhanVien = N'" + obj.TenNhanVien + "'")
                                       .FirstOrDefault();
                var resultMaNhaCungCap = db.Database
                                         .SqlQuery <String>("select MaNhaCungCap from dbo.NhaCungCap where TenNhaCungCap = N'" + obj.TenNhaCungCap + "'")
                                         .FirstOrDefault();
                PhieuDatHang phieuDatHang = new PhieuDatHang();
                phieuDatHang.MaPhieuDatHang = obj.MaPhieuDatHang;
                phieuDatHang.MaNhaCungCap   = resultMaNhaCungCap;
                phieuDatHang.MaNhanVien     = resultMaNhanVien;
                phieuDatHang.NgayChinhSua   = obj.NgayChinhSua;
                phieuDatHang.NgayDat        = obj.NgayDat;
                phieuDatHang.TongTien       = obj.TongTien;
                phieuDatHang.GhiChu         = obj.GhiChu;

                db.PhieuDatHangs.Add(phieuDatHang);

                if (db.SaveChanges() > 0)
                {
                    return(true);
                }
                return(false);
            }
        }
        public bool delete(String id)
        {
            using (CellphoneComponentEntities db = new CellphoneComponentEntities())
            {
                PhieuDatHang phieuDatHang = (from item in db.PhieuDatHangs
                                             where item.MaPhieuDatHang == id
                                             select item).SingleOrDefault();
                db.PhieuDatHangs.Remove(phieuDatHang);

                if (db.SaveChanges() > 0)
                {
                    return(true);
                }
                return(false);
            }
        }