Question

I am doing [this tutorial][1] over at http://www.asp.net. It is written for ASP.NET MVC 1. Although most of the stuff works for MVC 3, I do have a question regarding this code:

ASP.NET MVC 1.0 (straight from the tutorial)

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create([Bind(Exclude = "Id")] Contact contactToCreate)
{
    if (!ModelState.IsValid)
        return View();

    try
    {
        _entities.AddToContactSet(contactToCreate);
        _entities.SaveChanges();
        return RedirectToAction("Index");
    }
    catch
    {
        return View();
    }
}

ASP.NET MVC 3 (default Create action generated by MVC 3 Project, except my _entities object)

[HttpPost]
        public ActionResult Create(FormCollection collection)
        {
            try
            {
                _entities.AddToContacts(collection); // synax error
                _entities.SaveChanges();
                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

So my question is why do we pass Contact contactToCreate in the first case, but FormCollection collection in the second?

I could easily change argument in the second example to just Contact Contact contactToCreate, but I am curious as to what is this FormCollection collection stuff? Why did MVC 3 generate it for us? If it’s possible to use FormCollection instead, how would the modified example look like?
[1]: http://www.asp.net/mvc/tutorials/iteration-1-create-the-application-cs

Answer 1

FormCollection is the values entered by the user and Contact is the enderlying entity that you are creating.

Remember that this method is essentially called directly by the user as the result of a HTTP post and its bad practice to be blindly accepting user input without validating it. This and the fact that in real-world scenarios the values available to you in a HTTP post request don’t exactly match up to your data entity properties is probably the reason why its probably a good idea to accept a FormCollection (or other abstracted input representing your form values) rather than directly accepting an entity in your database.

Personally my modified example would look a little like this:

[HttpPost]
public ActionResult Create(FormCollection collection)
{
    try
    {
        var contactToCreate = validateAndCreateContact(collection);
        if (contactToCreate != null)
        {
            _entities.AddToContacts(collection);
            _entities.SaveChanges();
            return RedirectToAction("Index");
        }
    }
    catch (Exception ex)
    {
        // Logic to display error on the view goes here, e.g.
        base.ViewData["Exception"] = ex;
    }
    return View();
}

private Contact validateAndCreateContact(FormCollection collection)
{
    // Your implementation here
}

The validateAndCreateContact should validate user input and return a suitable Contact object if the input is all OK. If not it should return null and handle displaying a suitable error to the user (for example by setting properties on the ViewData).