如何将列表框值保存到 MVC4 和 EF 中的数据库中

我有一个注册表，允许管理员为特定用户选择菜单项。

我的目标是将选定的菜单项作为逗号分隔值保存到数据库中。

问题是MENU的值始终设置为 null，而不考虑更新模型。

用户.cs

public partial class User
{
    public User()
    {
        this.Mobilizations = new HashSet<Mobilization>();
    }  
    ...
    public string ADDRESS { get; set; }
    public string PHONE { get; set; }       
    public string MENU { get; set; }
 }

用户视图模型.cs

 public class userViewModel
{
    public User User { get; set; }       
    public SelectList MenuList { get; set; }
    [Required(ErrorMessage="Select some menu items")]
    public string[] MenuIds { get; set; }
}

控制器.cs

 [HttpPost]
    public ActionResult Create(userViewModel model)
    {           
       var menuIds = string.Join(",", model.MenuIds);
       var user = new User()
       {
           MENU=menuIds
       };           
        TryUpdateModel(model);
        if (ModelState.IsValid) //<= The value of MENU not getting updated
        {               
            _db.Entry(model.User).State = EntityState.Modified;
            _db.SaveChanges();
        }
        return RedirectToAction("Create");
    }

视图

   <div class="form-group">
        @Html.Label("Menu", new { @class = "col-sm-2 control-label " })
        <div class="col-sm-10 ">                
            @Html.ListBoxFor(model=>model.MenuIds,Model.MenuList,new {id="menuListBox", @class = "chosen-select",multiple="multiple",
            style="width:350px"})
            @Html.ValidationMessageFor(model =>model.MenuIds)
        </div>
    </div>

[HttpPost]
public ActionResult Create(userViewModel model)
{           
    TryUpdateModel(model);
    if (ModelState.IsValid) //<= The value of MENU not getting updated
    {               
        model.User.MENU = string.Join(",", model.MenuIds);
        _db.Entry(model.User).State = EntityState.Modified;
        _db.SaveChanges();
    }
    return RedirectToAction("Create");
}