Using custom ModelBinder to have strongly typed TPH models in controller actions-- is this smelly?

Question

Here's a little background on my solution:

• ASP.Net MVC app
• Using Linq-to-SQL with table-per-hierarchy inheritance
• Using DataAnnotationsModelBinder as default

So I have a Device abstract class and then a series of derived classes (ServerDevice, DiskDevice, PSUDevice, etc) that inherit from it in the proscribed Linq-to-SQL way. I have one controller that handles all these different related model types, and it renders different partials based on the type and a handy drop down to select them. My (GET) Create method looks like this:

// GET: /Devices/Create/3
public ActionResult Create(int? deviceTypeID)
{
    return View(DeviceFactory(deviceTypeID);
}

Where DeviceFactory is a static method returns a new instance of one of the derived classes based on an int discriminator. The POST Create method looks like this:

// POST: /Devices/Create
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create([ModelBinder(typeof(DeviceModelBinder))]Device device)
{
    if (!ModelState.IsValid)
            return View(device);

    _repository.Add(device);
    _repository.Save();
    TempData["message"] = string.Format("Device was created successfully.");
    return RedirectToAction(Actions.Index);
}

and my custom model binder looks like this:

public class DeviceModelBinder : DataAnnotationsModelBinder
{
    private readonly Dictionary<string, Type> _deviceTypes = 
                   new Dictionary<string, Type>
                  {
                      {"1", typeof (ServerDevice)},
                      {"2", typeof (DiskDevice)}
                      // And on and on for each derived type
                  };

    protected override object CreateModel(ControllerContext controllerContext,
        ModelBindingContext bindingContext, Type modelType)
    {
        return base.CreateModel(controllerContext, bindingContext,
        _deviceTypes[bindingContext.ValueProvider["deviceTypeID"].AttemptedValue]);
    }
}

So after trying to hook this up all day, reading about ActionInvoker, custom ActionFilters, and all sorts of other MVC stuff, I'm wondering if the solution I've arrived at is a good one. Help allay my fears that I'm missing some hugely obvious concept and re-inventing the wheel. Is there a better or more concise way?

Thanks!

Answer 1

My POV is it's "smelly" to bind entity/domain types to a UI at all. I explained this in considerably more detail in this answer. IMHO you should nearly always use dedicated presentation models. It is a nice side benefit that model binding do a presentation model is considerably easier, but the more important benefits are discussed in the linked answer.