ASP.Net MVC Where do you convert from Entities to ViewModels?

Question

Title pretty much explains it all, its the last thing I'm trying to work into our project. We are structured with a Service Library which contains a function like so.

        /// <summary>
        /// Returns a single category based on the specified ID.
        /// </summary>
        public Category GetCategory(int CategoryID)
        {
            var RetVal = _session.Single<Category>(x => x.ID == CategoryID);
            return RetVal;
        }

Now Category is a Entity (We are using Entity Framework) we need to convert that to a CategoryViewModel.

Now, how would people structure this? Would you make sure the service function returned a CategoryViewModel? Have the controller pull the data from the service then call another function to covnert to a view model?

Answer 1

Here's an excerpt from a blog post I wrote:

[AutoMap(typeof(IEnumerable<User>), typeof(IEnumerable<UserViewModel>))]
public ActionResult Index()
{
    // return all users
    IEnumerable<User> users = Repository.GetUsers();
    return View(users);
}

In this case the corresponding view is strongly typed to IEnumerable<UserViewModel>. It uses AutoMapper to define conversion rules between entities and view models. As for the [AutoMap] attribute, it's a custom action filter which inspects the model passed to the view and applies the proper conversion so that the view has only the view model.