AutoMapper problem with Dropdown - asp.net-mvc-3

Question

I´m started to work with AutoMapper today...
But I´m having some problem with Dropdown model...
What I have so far :
User Model
public class User : Entity
{
public virtual string Name { get; set; }
public virtual string Email { get; set; }
public virtual string Password { get; set; }
public virtual Role Role { get; set; }
}
Role Model
public class Role : Entity
{
public virtual string Name { get; set; }
}
UserUpdateViewModel
public class UserUpdateViewModel
{
public int Id{get;set;}
[Required(ErrorMessage = "Required.")]
public virtual string Name { get; set; }
[Required(ErrorMessage = "Required."), Email(ErrorMessage = "Email Invalid."), Remote("EmailExists", "User", ErrorMessage = "Email already in use.")]
public virtual string Email { get; set; }
[Required(ErrorMessage = "Required.")]
public virtual string Password { get; set; }
[Required(ErrorMessage = "Required")]
public virtual string ConfirmPassword { get; set; }
[Required(ErrorMessage = "Required.")]
public int RoleId { get; set; }
public IList<Role> Roles { get; set; }
}
UserController
public ActionResult Update(int id=-1)
{
var _user = (_userRepository.Get(id));
if (_user == null)
return RedirectToAction("Index");
Mapper.CreateMap<User, UserUpdateViewModel>();
var viewModel = Mapper.Map<User, UserUpdateViewModel>(_user);
viewModel.Roles = _roleRepository.GetAll();
return View(viewModel);
}
[HttpPost, Transaction]
public ActionResult Update(UserViewModel user)
{
if (ModelState.IsValid)
{
user.Password = _userService.GetPasswordHash(user.Password);
Mapper.CreateMap<UserViewModel, User>();
var model = Mapper.Map<UserViewModel, User>(user); //model.Role = null
_userRepository.SaveOrUpdate(model); //ERROR, because model.Role = null
return Content("Ok");
}
return Content("Erro").
}
View Update
...
#Html.DropDownListFor(model => model.RoleId, new SelectList(Model.Roles, "Id", "Name"), "-- Select--", new { #class = "form radius" })
...
Some considerations:
1 - I´m returning Content() because is all Ajax enabled using HTML 5 PushState etc etc
2 - In my Update(POST one) method, my model returned by Autommapper has Role = null
Why my Role returned by Automapper is null?
Is that the right way to work with AutoMapper? Any tip?
Thanks

Answer 1

The map is failing because you are trying to map a single Role directly to a collection of Roles. And a collection of Roles back to a single Role. You cant directly map between these as they are different types.
If you wanted to map a Role to a List then you could use a custom value resolver.
Mapper.CreateMap<User , UserUpdateViewModel>()
.ForMember(dest => dest.Roles, opt => opt.ResolveUsing<RoleToCollectionResolver>())
Public class RoleToCollectionResolver: ValueResolver<User,IList<Role>>{
Protected override IList<Role> ResolveCore(User source){
var roleList = new List<Role>();
roleList.Add(source.Role);
Return roleList;
}
}