public ActionResult XoaSP(int iMaSP)
        {
            List <SamPhamGH> lstSP = LayGioHang();
            SamPhamGH        SP    = lstSP.Find(n => n.BookId == iMaSP);

            lstSP.Remove(SP);
            Session["GioHang"] = lstSP;
            return(Json(lstSP, JsonRequestBehavior.AllowGet));
        }
        public ActionResult ThemGioHang(int iMaSP, int?SL)
        {
            List <SamPhamGH> lstSP = LayGioHang();
            SamPhamGH        SP    = lstSP.Find(n => n.BookId == iMaSP);

            if (SP == null)
            {
                SP = new SamPhamGH();
                Book sp = db.Books.Single(n => n.BookId == iMaSP);
                SP.BookId = iMaSP;
                SP.Title  = sp.Title;
                SP.ImgUrl = sp.ImgUrl;
                SP.Price  = double.Parse(sp.Price.ToString());
                if (SL == null)
                {
                    SP.SoLuongMua = 1;
                }
                else
                {
                    SP.SoLuongMua = int.Parse(SL.ToString());
                }
                lstSP.Add(SP);
                Session["GioHang"] = lstSP;
                return(Json(lstSP, JsonRequestBehavior.AllowGet));
            }
            else
            {
                if (SL == null)
                {
                    SP.SoLuongMua++;
                }
                else
                {
                    SP.SoLuongMua = int.Parse(SL.ToString());
                }
                Session["GioHang"] = lstSP;
                return(Json(lstSP, JsonRequestBehavior.AllowGet));
            }
        }