asp.net-mvc - Asp.net MVC ModelState.Isvalid 为 Id 返回 false

Question

我在看这个ASP.NET MVC course .我有一个 customer model具有以下属性。

public class Customer {
    public int Id { get; set; }
    [Required]
    [StringLength(255)]        
    public string Name { get; set; }

    [Display(Name = "Date of Birth")]
    public DateTime? DateOfBirth { get; set; }

    public bool IsSubscribedToNewsLetter { get; set; }


    public MembershipType MembershipType { get; set; }

    [Display(Name="Membership Type")]
    public byte? MembershipTypeId { get; set; }
}

请注意，Id 没有 Required数据注释。但在我的数据库中，Id 是主键，Identity 是列的真值。
有一个 ViewModel组成 Customer和 MembershipType楷模。

    public class CustomerFormViewModel {
        public IEnumerable<MembershipType> MembershipTypes { get; set; }
        public Customer Customer { get; set; }
    }

我有一个创建 new Customer 的 View 与 Name , DateOfBirth , MembershipType和 IsSubscribedToNewsLetter领域。它需要 CustomerFormViewModel .

@using Vidly.Models
@model Vidly.ViewModel.CustomerFormViewModel
@{
    ViewBag.Title = "New";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>@ViewBag.Message</h2>
@using (Html.BeginForm("Save", "Customer")) {
    <div class="form-group">
        @Html.LabelFor(m => m.Customer.Name,new{@class="control-label"})
        @Html.TextBoxFor(m => m.Customer.Name, new { @class = "form-control" })
        @Html.ValidationMessageFor(m=>m.Customer.Name)
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.Customer.DateOfBirth, new { @class = "control-label"})
        @Html.TextBoxFor(m => m.Customer.DateOfBirth,"{0:d MMM yyyy}", new { @class = "form-control" })
    </div>

    <div class="form-group">
        @Html.LabelFor(m => m.Customer.MembershipTypeId, new { @class = "control-label"})
        @Html.DropDownListFor(m => m.Customer.MembershipTypeId,new SelectList(Model.MembershipTypes,"Id","Name"), "Select Membership Type", new { @class = "form-control" })
    
    </div>
    <div class="checkbox">
        <label>
            @Html.CheckBoxFor(m => m.Customer.IsSubscribedToNewsLetter) Subscribed To Newsletter?
        </label>

    </div>

    @Html.HiddenFor(m=>m.Customer.Id)
    <button type="submit" class="btn btn-primary">Save</button>
}

这是我的 Save Controller :

    public ActionResult Save(Customer customer) {
        if (!ModelState.IsValid) {
            var viewModel = new CustomerFormViewModel {
                Customer = customer,
                MembershipTypes = _context.MembershipTypes.ToList()
            };
            return View("CustomerForm", viewModel);
        }
        if (customer.Id == 0 || customer.Id==null) {
            _context.Customers.Add(customer);
        }
        else {
            var CustomerInDb = _context.Customers.Single(c => c.Id == customer.Id);
            CustomerInDb.Name = customer.Name;
            CustomerInDb.DateOfBirth = customer.DateOfBirth;
            CustomerInDb.IsSubscribedToNewsLetter = customer.IsSubscribedToNewsLetter;
            CustomerInDb.MembershipTypeId = customer.MembershipTypeId;
        }
        _context.SaveChanges();
        return RedirectToAction("Index", "Customer");
    }

当我填写 CustomerForm查看并单击提交按钮， ModelState.Isvalid()方法总是错误的；结果第一个 if statement的 Save方法正确。所以我不能存储任何新客户。
我试过 debug通过放置 breakpoint 申请在 if (!ModelState.IsValid)并看到 Id字段正在创建错误(说“Id 字段是必需的”)。为什么说 Id不需要时需要吗？是否 ModelState.IsValid方法在数据库级别检查模型？我不这么认为。
如果我更改 Customer模型 Id像这样的属性: public int? Id { get; set; }并通过此更改 if 语句， if ((!ModelState.IsValid) && (customer.Id==null) )该应用程序运行良好。
是否有其他解决方案 Id问题？

Answer 1

我看了同样的类(class)，我猜作者在你看过之后更新了，因为他展示了这种确切类型的问题。问题是，当将 View 模型返回到新操作的 View 时，客户属性未初始化，因此 Id 为空，因此在尝试保存时 ModelState 失败

只需更改如下，以便在设置 viewModel 时，您初始化 Customer，然后 Id 为 0:

 public ActionResult New()
    {
        var memberShipTypes = _context.MembershipTypes.ToList();

        var viewModel = new CustomerViewModel
        {
            Customer = new Customer(),
            MembershipTypes = memberShipTypes
        };

        return View("CustomerForm", viewModel);
    }