C# 需要访问和编辑数据库中的属性

订单是用这种方法创建和保存的

public async Task<ActionResult> FirstClassCreate(FormCollection values)
    {
        var order = new Order();
        TryUpdateModel(order);
        var customer = db.Users.FirstOrDefault(x => x.Email == User.Identity.Name);
        var cart = ShoppingCart.GetCart(this.HttpContext);

        try
        {
            order.DeliveryDate = DateTime.Now.AddDays(1);

            order.DeliveryMethod = "First Class";
            order.FirstName = customer.FirstName;
            order.LastName = customer.LastName;
            order.PostalCode = customer.PostalCode;
            order.State = customer.State;
            order.City = customer.City;
            order.Email = customer.Email;
            order.Country = customer.Country;
            order.Phone = customer.PhoneNumber;
            order.Address = customer.Address;
            order.HasPaid = false;
            order.Username = customer.Email;
            order.OrderDate = DateTime.Now;
            var currentUserId = User.Identity.GetUserId();
            order.Total = cart.GetFirstClass();

            if (order.SaveInfo && !order.Username.Equals("guest@guest.com"))
            {
                var manager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));
                var store = new UserStore<ApplicationUser>(new ApplicationDbContext());
                var ctx = store.Context;
                var currentUser = manager.FindById(User.Identity.GetUserId());

                //Save this back
                //http://stackoverflow.com/questions/20444022/updating-user-data-asp-net-identity
                //var result = await UserManager.UpdateAsync(currentUser);
                await ctx.SaveChangesAsync();

                await storeDB.SaveChangesAsync();
            }

            //Save Order
            storeDB.Orders.Add(order);
            await storeDB.SaveChangesAsync();

            //Process the order
            cart = ShoppingCart.GetCart(this.HttpContext);
            order.Total = cart.GetFirstClass();

            order = cart.CreateOrder(order);

            return RedirectToAction("FirstClass", "Checkouts", order);
        }
        catch
        {
            //Invalid - redisplay with errors
            return View(order);
        }
    }   

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如果我理解正确，您不知道如何查询要更新的记录。因此，您需要使用

Where（）

过滤记录，并使用

Max（）

函数获取最新日期

var orderToBeChanged = db.Orders
    .Where(o => o.HasPaid == false && o => o.Email == User.Identity.Name)
    .Max(o => o.OrderDate);

---

您面临什么问题，或者希望有人代表您编写代码？您的问题很不清楚。你这样做到底有什么问题？你有例外吗？或者结果是否未存储到数据库中？或者你还有什么问题？唯一意味着只有1个，为什么你需要进一步过滤？您的结构中没有OrderID吗？有一个订单id，但它链接到用户的电子邮件，因此如果用户有多个订单，这将是一个问题

var orderToBeChanged = db.Orders
    .Where(o => o.HasPaid == false && o => o.Email == User.Identity.Name)
    .Max(o => o.OrderDate);