ASP.NET MVC - Null Object in ViewModel on POST

Question

Upon POST of an ActionController I am receiving the great ole' object reference not set to an instance of an object error.

Basically I need the ID of the userRequest to be saved WITH the requestResponse. (Foreign Key here)

Here is the code.

ViewModel:

public class RequestResponseViewModel
{
    public Models.Request userRequest { get; set; }

    public Models.RequestResponse requestResponse { get; set; }

}

View: In debug here there is value in model.userRequest.ID

    @model UserRequests.ViewModels.RequestResponseViewModel

  @{
    ViewBag.Title = "Create";
  }

  <h2>Admin Response to Request</h2>

  @using (Html.BeginForm())
  {
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.requestResponse.Response, 
  htmlAttributes: new { @class = "control-label col-md-1" })
            <div class="col-md-10">
                @Html.TextAreaFor(model => model.requestResponse.Response, new { 
  @class = "form-control", @rows = 5 })
                @Html.ValidationMessageFor(model => 
  model.requestResponse.Response, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
              @Html.LabelFor(model => model.userRequest.ID, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-2">

                @Html.DisplayFor(model => model.userRequest.ID)             
                @Html.ValidationMessageFor(model => model.userRequest.ID, "", new { @class = "text-danger" })
            </div>
            @Html.LabelFor(model => model.requestResponse.Author, htmlAttributes: new { @class = "control-label col-md-1" })
            <div class="col-md-3">
                @Html.EditorFor(model => model.requestResponse.Author, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.requestResponse.Author, "", new { @class = "text-danger" })
            </div>
            @Html.LabelFor(model => model.requestResponse.CreateDate, htmlAttributes: new { @class = "control-label col-md-1" })
            <div class="col-md-3">
                <h5>@DateTime.Now</h5>
                @Html.ValidationMessageFor(model => model.requestResponse.CreateDate, "", new { @class = "text-danger" })
            </div>
        </div>



        <div class="form-group">
            <div class="col-md-offset-1">
                <button type="reset" class="btn btn-default">Cancel</button>
                <input type="submit" value="Create" class="btn btn-success" />
            </div>
        </div>
    </div>

    <hr />
    <h3 class="text-success">Original Request</h3>
    <div class="row">
        <div class="col-md-10">
          <h4>@Html.DisplayFor(model => model.userRequest.Title)</h4>
        </div>
    </div>

    <div class="row">
        <div class="col-md-10">
            <h4>@Html.DisplayFor(model => model.userRequest.Description)</h4>
        </div>
    </div>

    }

    <div>
      @Html.ActionLink("Back to Browse", "Browse","Change")
    </div>

Get ActionResult:

public ActionResult Create(int id)
    {


        UserRequestContextDataContext db = new UserRequestContextDataContext();
        var request = (from m in db.Requests
                       where m.ID == id
                       select new Models.Request()
                       {

                           ID = m.ID,
                           Title = m.Title,
                           Description = m.Description,
                           BusinessUnit = m.BusinessUnit,
                           Author = m.Author,
                           ModuleName = m.MenuItem,
                           RequestStatus = 2,
                           SubmitDate = m.SubmitDate,
                           Type = m.Type,
                           UrgencyNum = m.UrgencyLevel


                       }).FirstOrDefault();

        var reqResponse = new Models.RequestResponse();


        var viewModel = new RequestResponseViewModel
        {
            userRequest = request,
            requestResponse = reqResponse

        };

        return View(viewModel);
    }

The "viewModel" here has everything I need. It's lost somewhere between the ActionResults..

And Finally the Post ActionResult:

 [HttpPost]
    public ActionResult Create(RequestResponseViewModel _requestResponseViewModel) 
    {
        try
        {

            if (ModelState.IsValid)
            {
                using (UserRequestContextDataContext db = new UserRequestContextDataContext())
                {

                    RequestResponse reqRes = new RequestResponse();
                    reqRes.Response = _requestResponseViewModel.requestResponse.Response.ToString();

                    reqRes.RequestID = _requestResponseViewModel.userRequest.ID;
                    reqRes.Author = _requestResponseViewModel.requestResponse.Author.ToString();
                    reqRes.CreateDate = DateTime.Now;

                    db.RequestResponses.InsertOnSubmit(reqRes);
                    db.SubmitChanges();
                }
            }

            return RedirectToAction("Browse","Change");
        }
        catch (Exception ex)
        {

            return View("Error", new HandleErrorInfo(ex, "Change", "Create"));
        }
    }

Using debug mode the userRequest object is NULL in the view model parameter of the POST method but requestResponse is FINE and populated as should.

Searching on this, it seemed most had issues with the naming convention in the view model but I've made sure there are no discrepancies there.

If there is a more clear way to do this workflow please mention.

Answer 1

Another reason the object could be NULL in the POST is due to forgetting to add the setters { get; set; } in your view model:

public Orders orders; --> missing { get; set; }

public class OrderViewModel
{
    public Orders orders { get; set; }

    public List<VendorJobTitleView> Jobs { get; set; }

    public List<ManagerView> Managers { get; set; }


}

Answer 2

@Html.DisplayFor does not create an HTML input element, but a simple string literal (for most types, some exceptions are listed in the docs: https://msdn.microsoft.com/en-us/library/ee407420(v=vs.118).aspx#Anchor_1). So when you press submit, your browser will not send the ID back to the server because it sends only form data (e.g. data from input, textare, select fields). Using your browsers developer tools (F12) you can examine what is actually send to the server.

You can add a hidden input field using @Html.HiddenFor(model => model.userRequest.ID) or use a custom display template for the ID to automatically add a hidden input field. You could further use UIHint attributes to automatically select a display template. Both approaches are thoroughly documented (e.g. http://www.codeguru.com/csharp/.net/net_asp/mvc/using-display-templates-and-editor-templates-in-asp.net-mvc.htm).