MVC编辑对象不起作用

我使用实体框架，我有两个类:

    public class User
    {
            public int UserID { get; set; }
            public string FirstName { get; set; }
            public string LastName { get; set; }
            public string Email { get; set; }
            public string UserName { get; set; }
            public string Password { get; set; }
            public int PermissionGroupID { get; set; }
            public string Comments { get; set; }
            public virtual PermissionGroup PermissionGroup { get; set; }
    }
public class PermissionGroup
{
        public int PermissionID { get; set; }
        public string PermissionValue { get; set; }
}

当然，在我的数据库中，我在User之间有FK。PermissionGroupID和PermissionGroup。PermissionID

现在，我试图做编辑控制器和视图使用UserModel:

public class UserModel
{
    public User User { get; set; }
    public SelectList PermissionGroups { get; set; }
    public int SelectedPermissionGroup { get; set; }
}

与控制器:

   public ActionResult Edit(int id = 0)
    {
        UserModel model = new UserModel ();
        model.User= managerUser.GetObjectById(id);
        model.PermissionGroups = new SelectList(managerPermission.GetAllList(), "PermissionID ", "PermissionValue");
        if (model.User== null)
        {
            return HttpNotFound();
        }
        model.SelectedPermissionGroup = model.User.PermissionGroupID;
        return View(model);
    }
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(UserModel model)
    {
        if (ModelState.IsValid)
        {
            model.User.PermissionGroupID = model.SelectedPermissionGroup;
            managerUser.EditObject(model.User);
            return RedirectToAction("Index");
        }
        UserModel newModel = model;
        newModel.User = managerUser.GetObjectById(model.UserID);
        newModel.PermissionGroups = new SelectList(managerPermission.GetAllList(), "PermissionID ", "PermissionValue");
        return View(newModel);
    }

管理器中的EditObject是这样的:

public virtual int EditObject(T objToEdit)
{
    DbEntities.Set<T>().Attach(objToEdit);
    DbEntities.Entry(objToEdit).State = EntityState.Modified;
    return DbEntities.SaveChanges();
}

在我看来，我不会把所有的东西都放进去，这是我所拥有的:

@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)
    <fieldset>
        <legend>User</legend>
        @Html.HiddenFor(model => model.User.UserID)
//Everything else to edit about the user....
        <div class="form-group">
            @Html.LabelFor(model => model.User.PermissionGroupID)
            @Html.DropDownListFor(model => model.SelectedPermissionGroup, Model.PermissionGroups, new { @class = "form-control" })
            <p class="help-block">@Html.ValidationMessageFor(model => model.User.PermissionGroupID)</p>
        </div>
        <p>
            <input type="submit" value="Save" />
            @Html.ActionLink("Back", "Index")
        </p>
    </fieldset>
}

所以，当我点击"保存"，根据我的断点，它传递一切正确，但在用户类的PermissionGroup属性不填充为PermissionGroupID(它确实从选择的下拉菜单接收ID。然后它返回到索引视图但是没有我做的任何改变。

我在其他项目中使用了完全相同的EditObject方法，它工作得很好，与下拉列表和所有。

我错过了什么?

@Html.DropDownListFor(model => model.SelectedPermissionGroup, 
                      Model.PermissionGroups, 
                      new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.User.PermissionGroupID)

@Html.DropDownListFor(model => model.User.PermissionGroupID, 
                               Model.PermissionGroups, 
                               new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.User.PermissionGroupID)