Commenting strategies in C# & asp.net web api

I've been working on a ASP.NET Web Api 2 project as a learning exercise, and I was wondering what the norm regarding commenting is.

I use the Repository / Service Pattern, and everything is very much decoupled, which results in having a large number of classes whose purpose is pretty clear. I also name my variables in a way that they explain themselves.

This leaves me wondering what I should actually be commenting in this scenario.

• Should I just stick to class-summaries ( even if the class itself is self-explanatory ) ?
• What about self-explanatory methods ?
• Do data / business entity classes need a summary ?
• What about interfaces ?

To give a bit more context, here is one of my repository classes which provides CRUD functionality:

public class UserRepository : RepositoryBase<User, decimal>
{
    private readonly ShortStuffContext _context;

    public UserRepository(ShortStuffContext context)
    {
        _context = context;
    }

    public override IEnumerable<User> GetAll()
    {
        return _context.Users.BuildUser();
    }

    public override User GetById(decimal id)
    {
        return _context.Users.FirstOrDefault(u => u.Id == id).BuildUser();
    }

    public override CreateStatus<decimal> Create(User entity)
    {
        if (_context.Users.Any(u => u.Id == entity.Id))
        {
            return new CreateStatus<decimal> { status = CreateStatusEnum.Conflict };
        }

        var user = new Data.Entities.User();
        user.InjectFrom<SmartConventionInjection>(entity);
        _context.Users.Add(user);
        _context.SaveChanges();

        return new CreateStatus<decimal> { status = CreateStatusEnum.Created, Id = user.Id };
    }

    public override UpdateStatus Update(User entity)
    {
        var dbUser = _context.Users.FirstOrDefault(u => u.Id == entity.Id)
                             .InjectFrom<NotNullInjection>(entity);

        if (dbUser != null)
        {
            var changeTrackerUser = _context.ChangeTracker.Entries<Data.Entities.User>()
                            .FirstOrDefault(u => u.Entity.Id == entity.Id);

            changeTrackerUser.CurrentValues.SetValues(dbUser);
            if (_context.SaveChanges() == 0)
            {
                return UpdateStatus.NoChange;
            }
            return UpdateStatus.Updated;
        }
        return UpdateStatus.NotFound;
    }

    public override void Delete(decimal id)
    {
        var user = _context.Users.FirstOrDefault(u => u.Id == id);
        _context.Users.Remove(user);
        _context.SaveChanges();
    }
}

So in a class like that, is it worthwhile to put a summary like "Provides CRUD functionality for the User Data Entity" ( and then repeat that summary for every other repository ), or not ? What about method comments, or inline comments?

Edit: My project is on Github. I know about adding comments to more complex methods, and I'm planning on adding comments to the Extensions and the ValueInjecter classes soon ( which hold by far the most complex code ). Apart from that, any advice regarding where to put comments is very much welcome.