模型State.IsValid返回false的麻烦

Question

在使用Entity Framework的ASP.NET中，我试图将新条目添加到名为Provider的数据库中。视图从另一个表返回默认值UserID和类别作为外键。当我调试控制器时Post方法有一个if（ModelState.IsValid），它一直返回false。无法理解为什么我可能不完全理解ModelState及其工作原理。

当我将if（ModelState.IsValid）覆盖为if（true）时，它成功地将新条目添加到数据库中并正确设置了所有字段。

当我验证当地人时，它提供以下内容:(由于没有足够的声誉来使用图像格式，我选择将图片作为链接放置）https://i.ibb.co/2Yrz4d8/debugging-ASP.png

ModelState.IsValid = false

providers             | {MAR.Models.Providers}
providers.ID          | 0
Providers.UserID      | "003f528f-f8..."
providers.VisitAvail  | null
providers.VisitType   | null
providers.VisitTypeID | 1

模型：

public class Providers
    {
        public int ID { get; set; }
        public string UserID { get; set; }
        public int? VisitTypeID { get; set; }
        public virtual VisitTypes VisitType { get; set; }
        public virtual ICollection<VisitAvailabilitys> VisitAvailability { get; set; } 
    }

public class VisitTypes
    {
        public int ID { get; set; }
        public string Description { get; set; }
        public int? SiteID { get; set; }
        public virtual Sites Site { get; set; }
        public int? StatusID { get; set; }
        public virtual Status Status { get; set; }
        public virtual ICollection<Appointments> Appointment { get; set; }
        public virtual ICollection<VisitReasons> VisitReason { get; set; }
        public virtual ICollection<Providers> Provider { get; set; }
    }

控制器：

        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Assign([Bind(Include = "ID,UserId,VisitTypeID")] Providers providers)
        {

            if (ModelState.IsValid)
            {
                db.Providers.Add(providers);
                db.SaveChanges();
                return RedirectToAction("Index");
            }
            ManageMessageId? message;
            message = ManageMessageId.NotAssign;
            return RedirectToAction("Index", new { Message = message });//providers
        }

视图：

<div class="form-group">
            @Html.LabelFor(model => model.UserID, "User ID" ,htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.UserID, new { htmlAttributes = new { @class = "form-control", @readonly = "readonly", @Value = ViewBag.UserId } })
                @Html.ValidationMessageFor(model => model.UserID, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.VisitTypeID, "Type of provider", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.VisitTypeID, null, htmlAttributes: new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.VisitTypeID, "", new { @class = "text-danger" })
            </div>
        </div>

我的预期结果是ModelState.IsValid为true。

Answer 1

将光标指向ModelState对象，我敢肯定，它会显示确切的错误。