ASP.NET MVC5 无效的模型状态:如何将外键传递到下拉列表并将其传递回 HTTPPost

我有一个项目模型，如下所示：

public class Project
{
    public int Id { get; set; }
    ....
    [Required]
    public virtual ApplicationUser Client { get; set; }
    [Key]
    [ForeignKey("Client")]
    public string ClientID;

    [Required]
    public virtual ApplicationUser ProjectManager { get; set; }
    [Key]
    [ForeignKey("ProjectManager")]
    public string ProjectManagerID;
    ....

}

在尝试将具有指定角色的用户传递到创建操作中，如下所示，使用 ViewBag：

// GET: /Project/Create
public ActionResult Create()
{
    populateRoles();
    SelectList PMs = new SelectList(projectManagers, "Id", "Name");
    ViewBag.ProjectManagerID = PMs;
    SelectList Clients = new SelectList(clients, "Id", "Name");
    ViewBag.ClientID = Clients;
    return View();
}

这是下拉菜单的剃刀视图部分：

<div class="form-group">
    @Html.Label("Project Manager", new { @class = "col-md-2 control-label" })
    <div class="col-md-10">
        @Html.DropDownList("ProjectManagerID", ViewBag.ProjectManagerID as SelectList, new { @class = "col-md-10 control-label" })
    </div>
</div>
<div class="form-group">
    @Html.Label("Client", new { @class = "col-md-2 control-label" })
    <div class="col-md-10">
        @Html.DropDownList("ClientID", ViewBag.ClientID as SelectList, new { @class = "col-md-10 control-label" })
    </div>
</div>

到目前为止没有问题，但是在表单发布中，我的模型将没有有效状态：

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "Id,Name,Progress,CreateDate")] Project project)
{
    /*---------------------populate select lists ------*/
    populateRoles();
    SelectList PMs = new SelectList(projectManagers, "Id", "Name");
    ViewBag.ProjectManagerID = PMs;
    SelectList Clients = new SelectList(clients, "Id", "Name");
    ViewBag.ClientID = Clients;
    /*-----------try to fix invalid modelstate ---------*/
    string projectManagerID = Request["PMs"];
    string clientID = Request["Clients"];
    project.ProjectManagerID = projectManagerID;
    project.ClientID = clientID;
    if (ModelState.IsValid) // <-Invalid modelstate because required foreign key properties
    {
        dbContext.Projects.Add(project);
        dbContext.SaveChanges();
        return RedirectToAction("Index");
    }
    return View(project);
}

问题：如何在此处传递所需的外键属性？

    [HttpPost]
    public ActionResult Create(string submitButton)
    {
        var model = new MyClass();  // go and get the record you want to edit
        if (submitButton == "Save")
        {
            TryUpdateModel(model);
            if (!ModelState.IsValid) // if the modelstate isn't valid, setup the dropdowns for the return trip to the form
            {
                ViewData["OrganizationId"] = model.OrganizationId;
                ViewBag.RecordTypes = GetRecordTypes(model.OrganizationId);
                return View(model);
            }
            context.AddToMyType(model);
            context.SaveChanges(); // save changes if there are no errors
        }
        return RedirectToAction("Index", new { id = model.OrganizationId });
    }