MVC2 - Basic question where logic should go

Question

Starting with MVC2, messing around with a simple db and just using the index view to display the items like:

in the controller:

    //
    // GET: /Equipment/

    public ActionResult Index()
    {
        return View(database.Artists.ToList());
    }

then the auto generated code in the view:

        <td> <%: item.ArtistID %> </td>
        <td> <%: item.GenreID %> </td>

etc etc

In my example, its potential that this data hasn't been filled up, so it may be null. Now when I tried to load the view I will get a NullReferenceException. So where would the code for this belong ?

I guess you could have an if statement in the view, though surely this is not where the logic should go. Should I create a html helper which just returns empty string if the value is null?

edit:

Thanks for the help.

I have another query. What if say I'm developing a index browse type page. At the moment im displaying all items on the one page but there are like 2k items. Is there a tutorial or example of how to split this up? I guess my index browse controller could just take a integer range value from the browser, then I just say display next 100

Answer 1

When you return the list of artists you need to check for null and return a New list of Artists.

This is best accomplished, IMO, by returning what is called a ViewModel.

Class MyFormViewModel
    List<Artist> artists {get; set;}

then in your controller

MyFormViewModel fvm = new MyFormViewModel();

fvm.artists = database.Artists.ToList();
if (fvm.artists == null) fvm.artists = new List<Artist>();
return View(fvm)

Then your view inherits from MyFormViewModel

Then consider factoring out the logic in the cntroller that gets the artists and sets objects out to another layer

EDIT

The reason for the FormViewModel is because if you want to add other things to return to the view you simply extend the model making it very easy to add more partial views etc

EDIT 2

If you have a partial viwe call ArtistList which takes the full list of artists. It then simply itterates through the list of artists and renders another PV call say Artist which is given a single instance of artist.

Then you could do a simple check within the Artist partial view for a null.

Or you could check in the ArtistList partial view for a null record and render another PV called say NullArtist.

Answer 2

One option is to display a different view that is displayed when no artist was found, e.g. "No Artist Found.". In this case the change would be in the controller.

The other option is to modify the view so that it contains some code to either render the message that no artist was found if the list was empty or to render the list.

You can always get more sophisticated with a ViewModel if you need to later. At this stage there are simpler solutions.