如何从MVC5中的下拉菜单将值存储到数据库

Question

几天以来，我一直在学习ASP.NET MVC5，试图完成需要一些下拉菜单的proyect。 遗憾的是，我无法克服这个问题，也许有人可以给我一个提示。

因此，基本上，我要求所有用户进入数据库，并将它们显示在一个下拉菜单中，这很正常，但是当我在公式器上保存更改时，由于某种原因，所有值都正确存储在数据库中，而不是下拉列表中的值菜单。

Create.cshtml

    <div class="form-group">
        @if (ViewBag.Users != null)
        {
            @Html.LabelFor(model => model.Student, htmlAttributes: new { @class = "control-label col-md-2" })
            @Html.DropDownList("Users", "Student")
            @Html.ValidationMessageFor(model => model.Student, "", new { @class = "text-danger" })
        }
    </div>
----------------------

<div class="form-group">
    @if (ViewBag.Users != null)
    {
        @Html.LabelFor(model => model.Teacher, htmlAttributes: new { @class = "control-label col-md-2"})
        @Html.DropDownList("Users", "Teacher")
        @Html.ValidationMessageFor(model => model.Teacher, "", new { @class = "text-danger" })
    }
</div>

---

ClassesControler.cs

// GET: Classes/Create
        Entities2 database = new Entities2();

    public ActionResult Create()
    {
        List<AspNetUsers> Users = database.AspNetUsers.ToList();
        ViewBag.Users = new SelectList(Users, "UserName", "UserName");

        return View();
    }

    // POST: Classes/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see https://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "Id,StudentsReport,TeachersReport,Language,TeachersEarning,Student,Teacher,NumberOfClasses,ClassName")] Class @class)
    {

        if (ModelState.IsValid)
            {
                db.Classes.Add(@class);
                db.SaveChanges();

                return RedirectToAction("Index");
            }

        return View(@class);
    }

非常感谢你 ！

Answer 1

您不能设置整个Users对象。 只需设置UserId属性（外键），也许您必须将其添加到您的Classes模型中。

像这样：

Create.cshtml：

@Html.LabelFor(model => model.TeacherId, htmlAttributes: new { @class = "control-label col-md-2"})
@Html.DropDownList("TeacherId", null, "Please select", htmlAttributes: new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.TeacherId, "", new { @class = "text-danger" })

Controller.cs

public ActionResult Create()
{
    ...
    ViewBag.TeacherId = new SelectList(db.Users, "TeacherId", "TeacherName");
    return View();
}

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = ...,TeacherId,...")] Class class)
{
    ...
}