Say I have RegisterModel for user registration and some UserService that implementing IUserService
public interface IUserService
{
User CreateUser(User ne
You never pass a view model to a service. A service doesn't even know about the existence of a view model that you might have defined in your GUI (ASP.NET MVC) tier. A service works with domain models. Personally I use AutoMapper to map between view models and models and vice versa, so this logic goes into the mapping layer.