ASP.NET MVC5无效的ModelState：如何将外键传递给下拉列表，并将其传递回HTTPPost？

Question

I've a Project model like below:

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;

    ....


}

In tried to pass users with specified role inside create action like below,using 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();
}

And here is the part of Razor View for drop-downs:

<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>

There is no problem up to here, but on form post my model will not have valid state:

[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);
}

The Question: How to pass required foreign key properties here?

Answer 1

I don't believe you are using the framework in the correct fashion in your controller. Using Request items is leaving behind all of the things that the ASP.NET MVC framework is trying to do for you. It should really read along the following lines:

    [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 });
    }

The reality is that you should be allowing ASP.NET MVC to handle almost all of your binding. It's only in very particular circumstances that you should override it.

As an additional point, as Shyju also says in the comments, best practice dictates that you should also use a dedicated view model for this rather than your domain model.

PS Lecturing aside (sorry), the specific reason why your code is non-operational is that the ProjectManager property is not set at the time you are calling SaveChanges(). You have only set ProjectManagerID, this will not automagically set the ProjectManager property for you, you have to do that yourself if you don't use the bindings as intended in MVC.

Good luck with your app!