Question

I’m a bit confused about when using the “IRepository pattern”, when actually to load the data.

Currently I have something like this:

public class MainViewModel : ViewModelBase
{
    // EF4 generated ObjectContext 
    private ScorBotEntities context = new ScorBotEntities();         

    // Custom IUserRepository class
    private IUserRepository userRepository;

    public MainViewModel()
    {
        this.userRepository = new UserRepository(context.Users);
    }

    public ObservableCollection<User> Users
    {
        get
        {
            return new ObservableCollection<User>(userRepository.GetAll());
        }
    }
}

ScorBotEntities are autogenerated using EF4 (I had a look at POCOs, to much work for this sized project).

You can find the definition of the UserRepository here: http://code.google.com/p/i4prj4-g2/source/browse/ScorBotRobotics/ScorBotRobotics/Repositories/UserRepository.cs

But basically, what I’m wondering about is, why do it even make sense to use a repository here, instead of just writing it like this:

public class MainViewModel : ViewModelBase
{
    private ScorBotEntities context = new ScorBotEntities();         

    public MainViewModel()
    {
    }

    public ObservableCollection<User> Users
    {
        get
        {
            return new ObservableCollection<User>(context.Users);
        }
    }
}

It makes sense to abstract functionality away such as with the UsernameAndPassword method. But in that case, perhaps using some Query Objects would be more ideal?

Answer 1

Separation of concerns

What if you want to change the storage of ‘Users’, from say SQL to a flat file?

Then context would not be needed, and you’d have to change every use of it, instead of just your IRepository implementation.

Also, ideally you would have your IRepository injected. So you’re MainViewModel doesn’t care how it gets it’s Users.