AutoMapper Update Actions in ASP.NET MVC

Question

This is probably quite straight forward for some, however I'm a bit confused and can't find a decent example. Say I'm using view models and my POST action takes in that view model. Typically I would do something along the following lines:

    [HttpPost]
    public ActionResult Update(UserViewModel uvm)
    {
        User user = Mapper.Map<UserViewModel, User>(uvm);
        _repository.Update(user);

        return RedirectToAction("Index");
    }

Although this isn't the full picture. The mapping would work fine, however if I were to just update what I've mapped then it'd get rid of valuable data in the database because of course in this case I'm not updating the password or other details.

My repository looks something like this:

    public void Update(User user)
    {
        User u = Session.QueryOver<User>().Where(x => x.UserName == user.UserName).SingleOrDefault();

        if (u == null)
            throw new Exception("User not found");

        u.Forename = user.Forename;
        u.Surname = user.Surname;
        u.EmailAddress = user.EmailAddress;
    }

[I'm using NHibernate so it'll save the object back to the DB once the session is closed (after the request has finished) automatically for me.]

So my question is, in my repository should I load the "User" entity, then update the values I want, and then save it back, or is there another method to do this? The reason I ask is because it seems a bit... "manual" if you see what I mean? Perhaps it is correct, but I just wanted to see opinions of those with more experience in this area.

Cheers

Answer 1

I use the following approach:

[HttpPost]
public ActionResult Update(UserViewModel uvm)
{
    User user = _userRepository.FindById(uvm.Id);

    user.Forename = uvm.Forename;
    user.Surname = uvm.Surname;
    user.EmailAddress = uvm.EmailAddress;

    _userRepository.Update(user);

    return RedirectToAction("Index");
}

---

UPDATE:

To address the comments about AutoMapper here's how to proceed:

Let's take for example the following classes:

public class UserViewModel
{
    public string Forename { get; set; }
    public string Surname { get; set; }
    public string EmailAddress { get; set; }
}

public class User
{
    public string Forename { get; set; }
    public string Surname { get; set; }
    public string EmailAddress { get; set; }

    public string Password { get; set; }
}

We don't want to modify the user password in the UI. So we express our intention to AutoMapper:

Mapper
    .CreateMap<UserViewModel, User>()
    .ForMember(dest => dest.Password, opt => opt.Ignore());

and then:

[HttpPost]
public ActionResult Update(UserViewModel uvm)
{
    // Fetch the original model we would like to update
    User user = _userRepository.FindById(uvm.Id);

    Mapper.Map(uvm, user);
    // At this stage the user model will have its 
    // Forename, Surname and EmailAddress properties 
    // updated from the view model and its Password property
    // will remain the one we got from the repository

    _userRepository.Update(user);

    return RedirectToAction("Index");
}

---

UPDATE 2:

To address the question in the comments about configuring AutoMapper I usually use Profiles:

public class UsersProfile : Profile
{
    protected override void Configure()
    {
        Mapper
            .CreateMap<UserViewModel, User>()
            .ForMember(dest => dest.Password, opt => opt.Ignore());    

        Mapper
            .CreateMap<User, UserViewModel>();
    }
}

and then have a registry class which registers all the mappers:

public class MappingsRegistry
{
    public static void Configure()
    {
        Mapper.AddProfile(new UsersProfile());
        Mapper.AddProfile(new SomeOtherProfile());
        ...
    }
}

which is called in Application_Start:

MappingsRegistry.Configure();

Finally my controllers have a reference to the mapping engine:

public class UsersController : Controller
{
    private readonly IUsersRepository _repository;
    private readonly IMappingEngine _mappingEngine;
    public ContratsFCController(IUsersRepository repository, IMappingEngine mapperEngine)
    { 
        _repository = repository;
        _mapperEngine = mapperEngine;
    }

    [AutoMap(typeof(User), typeof(UserViewModel))]
    public ActionResult Update(int id)
    {
        var user = _repository.FindById(id);
        return View(user);
    }

    [HttpPost]
    public ActionResult Update(UserViewModel uvm)
    {
        if (!ModelState.IsValid)
        {
            return View(uvm);
        }
        var user = _repository.FindById(uvm.Id);
        _mapperEngine.Map(uvm, user);
        _repository.Update(user);
        return RedirectToAction("Index");
    }
}

Now all that's left is to instruct your DI framework to pass the Mapper.Engine property to the constructor and in your unit tests obviously substitute them with an appropriate mock.