ViewModel getting null values in action method

Question

I am using a ViewModel to retrieve entered data in controller action. But the ViewModel is getting empty values in it's properties. I am creating one partial view

and in that partial view I am creating drop down lists by binding the ViewModel and then I'm rendering that partial view in other View

Below is my code

My ViewModel :

public class LookUpViewModel
    {
        RosterManagementEntities rosterManagementContext = new RosterManagementEntities();
        public  LookUpViewModel()
        {

            tblCurrentLocations = from o in rosterManagementContext.tblCurrentLocations select o;
            tblStreams = from o in rosterManagementContext.tblStreams select o;   
        }

        [Required]
        public virtual IEnumerable<tblCurrentLocation> tblCurrentLocations { get; set; }

 [Required]
        public virtual IEnumerable<tblStream> tblStreams {  get;  set; }

My Partial View:

@model PITCRoster.ViewModel.LookUpViewModel

@Html.Label("Location")
@Html.DropDownListFor(M=>M.tblCurrentLocations, new SelectList(Model.tblCurrentLocations, "LocationId", "Location"), "Select Location")
@Html.ValidationMessageFor(M=>M.tblCurrentLocations)
<br />
@Html.Label("Stream")

@Html.DropDownListFor(M => M.tblStreams, new SelectList(Model.tblStreams, "StreamId", "Stream"), "Select Streams")
@Html.ValidationMessageFor(M => M.tblStreams)

My View in which I am rendering this above partial view

@{
    ViewBag.Title = "Resources";
}
<script src="~/Scripts/jquery.validate.min.js"></script>
<script src="~/Scripts/jquery.validate.unobtrusive.min.js"></script>
<h2>Resources</h2>

@using (Html.BeginForm("AddResource", "Resources", FormMethod.Post))
{

    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)
    Html.RenderPartial("_LookUpDropDowns", new PITCRoster.ViewModel.LookUpViewModel());

    <br />
    <input type="submit" value="Create" />
}

And this is my controller action method : [HttpPost]

public void AddResource(LookUpViewModel testName)
        {
            //code
        }

When I put a debugger on my controller action method control goes to that Action method. But ViewModel object has null in it. I tried accessing entered values using FormCollection object and I'm getting all the data as expected...

Below is my code for controller action with FormCollection

 [HttpPost]
        public void AddResource(FormCollection form)
        {
            var x = form["tblStreams"]; //I get value here..
        }

Can anybody explain me why I'm not getting values in ViewModel object ? Thank you...

Answer 1

You cannot bind a dropdownlist to a collection of complex objects - in your case IEnumerable<tblCurrentLocation> and IEnumerable<tblStream>

A <select> tag only posts back a single value (the value of the selected option) so in the POST method the DefaultModelBinder is attempting to so testName.tblCurrentLocations = "1" (assuming the value of the selected option is 1) which of course fails and the property is set to null

You need a view model containing properties that you want to bind to (and ideally will include the SelectList's used by the DropDownListFor() helper)

public class LookUpViewModel
{
  [Display(Name = "Location")]
  [Required(ErrorMessage = "Please select a location")]
  public int SelectedLocation { get; set; }
  [Display(Name = "Stream")]
  [Required(ErrorMessage = "Please select a stream")]
  public int SelectedStream { get; set; }
  public SelectList LocationList { get; set; }
  public SelectList StreamList { get; set; }
}

Then in the view

@Html.LabelFor(m => m.SelectedLocation)
@Html.DropDownListFor(m => m.SelectedLocation, Model.LocationList, "-Please select-")
@Html.ValidationMessageFor(m => m.SelectedLocation)

@Html.LabelFor(m => m.SelectedStream)
@Html.DropDownListFor(m => m.SelectedStream, Model.StreamList, "-Please select-")
@Html.ValidationMessageFor(m => m.SelectedStream)

and in the controller

public ActionResult Edit()
{
  LookUpViewModel model = new LookUpViewModel();
  ConfigureViewModel(model);
  return View(model);
}

[HttpPost]
public ActionResult Edit(LookUpViewModel model)
{
  if (!ModelState.IsValid)
  {
    ConfigureViewModel(model);
    return View(model);
  }
  // model.SelectedLocation will contain the value of the selected location
  // save and redirect
}

private void ConfigureViewModel(LookUpViewModel model)
{
  // populate your select lists
  var locations = from o in rosterManagementContext.tblCurrentLocations select o;
  model.LocationList = new SelectList(locations, "LocationId", "Location");
  .... // ditto for streams
}

Note as also indicated in Maximilian's answer, your view model should only contain properties your need for the view. Your controller is responsible for populating the values. A view model should never make a call to a database - it should not even be aware that one exists.

Answer 2

This answer will not solve your problem directly, but first of all I recommend you to outsource the filling of the ViewModel at least to the controller (Because otherwise it will recreate the DBContext every time the constructor is called). A ViewModel should only contain data - no logic. And secoundly I would use the DBContext in an Using statement

ViewModel:

public class LookUpViewModel
    {    
        [Required]
        public virtual IEnumerable<tblCurrentLocation> tblCurrentLocations { get; set; }

        [Required]
        public virtual IEnumerable<tblStream> tblStreams {  get;  set; }

Controller:

public ActionResult Foo()
{
    LookUpViewModel ViewModel = new LookUpViewModel();
    using(RosterManagementEntities rosterManagementContext = new RosterManagementEntities())
    {
        ViewModel.tblCurrentLocations = from o in rosterManagementContext.tblCurrentLocations select o;
        ViewModel.tblStreams = from o in rosterManagementContext.tblStreams select o; 
    }

    return View(ViewModel);
}