public ItemGioHang(int iMaSP, int sl)
 {
     using (QLBH_SQLEntities db = new QLBH_SQLEntities())
     {
         this.MaSP = iMaSP;
         SANPHAM sp = db.SANPHAMs.Single(n => n.MaSP == iMaSP);
         this.TenSP     = sp.TenSP;
         this.DonGia    = sp.DonGia;
         this.HinhAnh   = sp.HinhAnh;
         this.SoLuong   = sl;
         this.ThanhTien = SoLuong * sp.DonGia;
     }
 }
 public ItemGioHang(int iMaSP)
 {
     using (QLBH_SQLEntities db = new QLBH_SQLEntities())
     {
         this.MaSP = iMaSP;
         SANPHAM sp = db.SANPHAMs.Single(n => n.MaSP == iMaSP);
         TenSP     = sp.TenSP;
         DonGia    = sp.DonGia;
         HinhAnh   = sp.HinhAnh;
         SoLuong   = 1;
         ThanhTien = SoLuong * DonGia;
     }
 }