Question

I am using MVC4 and EF5 codefirst. I have a problem whereby when creating a new data record with reference to a row with a foreign key, the fields of the foreign key row are set to null.

Here is a simplified scenario:

public class Person
{
  string name { get; set; }
  Color color { get; set; }
}

public class Color
{
  int id { get; set; }
  string name { get; set; }
}

The viewmodel:

public class PersonViewModel
{
    public Person Person { get; set; }
    public IEnumerable<SelectListItem> Colors { get; set; }

    public PersonViewModel()
    {
        Context db = new Context();
        Colors = db.Colors.ToList().Select(t => new SelectListItem() { Text = t.Name, Value = t.Id.ToString() });
    }
}

The controller:

public ActionResult Create()
{
    return View(new PersonViewModel);
}

[HttpPost]
public ActionResult Create(PersonViewModel personViewModel)
{
    if (ModelState.IsValid)
    {   
        db.Person.Add(personViewModel.Person);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(personViewModel);
}

and finally, the create view:

@model PersonViewModel
@using (Html.BeginForm())
{   
    @Html.ValidationSummary(true)

    @Html.LabelFor(model => model.Person.Name) 
    @Html.EditorFor(model =>  model.Person.Name)

    @Html.LabelFor(model => model.Person.Color)
    @Html.DropDownListFor(model => model.Person.Color.Id, this.Model.Colors)

    <input type="submit" value="Create" title="Create ticket" />
}

Say I have two colors in the data:
1. red
2. blue

When creating a new person through the view and selecting blue as the color, the person will be created correctly but ‘blue’ with id 2 in color table will maintain its ID (of 2) but its name will have been set to empty.

Im sure there is a binding issue occurring here? Should this be supported as standard in the framework or do I need to create my own modelbinder?

Thanks

Answer 1

So it turns out I wasn’t correctly following entity framework conventions. By explicitly defining the foreign key column, entity framework correctly recognises the relationship and works as I would expect. Therefore, the new data model (adding the explicit foreign key column)

public class Person
{
  string Name { get; set; }

  int ColorId { get; set; }     
  Color color { get; set; }
}

public class Color
{
  int ColorId { get; set; }
  string name { get; set; }
}

and the updated view (binding on the new foreign key column):

@model PersonViewModel
@using (Html.BeginForm())
{   
    @Html.ValidationSummary(true)

    @Html.LabelFor(model => model.Person.Name) 
    @Html.EditorFor(model =>  model.Person.Name)

    @Html.LabelFor(model => model.Person.Color)
    @Html.DropDownListFor(model => model.Person.ColorId, this.Model.Colors)

    <input type="submit" value="Create" title="Create ticket" />
}