Looking for the best way to provide a ViewModel on “Add new” View and just part of it / different one as its submit POST response

Question

I'm developing a Web Application by using ASP.Net MVC 5. My model is something similar to:

Person
    - int ID
    - string FullName
    - int PersonTypeId

PersonType
    - Id
    - Name
    - Description

I'm working on the "create new Person" page. I have created a ViewModel with the following structure:

public class SampleAddViewModel
{
    public Person person;
    public SelectList personTypes; // Used to populate the DropDown element.
}

My controller's GET method (to simply display the page):

// GET: Add new person
public ActionResult Add()
{
    SampleAddViewModel savm  = new SampleAddViewModel();
    AddPersonViewModel.personTypes = new SelectList(PersonTypesEntity.GetAll(), "Id", "Name");

    return View(savm);
}

In my controller's POST method (to store the created person) I would expect to just receive the Person model, and not the entire ViewModel. But on the View page I think it is only possible to declare an @model razon line, which I think it must be @model SampleAddViewModel ...

Would it be possible to, in the POST Add entry, have something similar to the following:

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Add([Bind(Include = "ID, Name, PersonTypeId")] Person person)
{
    if (ModelState.IsValid)
    {
        db.Add(person);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    x <- //Should I re-create the ViewModel in here?
    return View(x);
}

Which would be the best way to address the problem? I'm also trying to avoid using ViewBag. Maybe the best way in fact is to re-send the entire ViewModel.

Answer 1

If you have any errors on the server side on the POST method then yes, you'd want to send the ViewModel back to the view.

Since you are only sending a Person instance into the controller action and your View is expecting an instance of SampleAddViewModel , you should create an instance of one of these and pass it to the View; After all, you're going to need to repopulate the personTypes dropdown with data again.