How to do Lists in a view model? + dataannotations

Question

I am using asp.net mvc 3, data annotations and auto mapper.

I want to have all my annotations on properties in my view model once the properties pass validation I use auto mapper to map it back to my domain object.

I have a viewmodel that has properties that I want to have a collection of since I want to generate a table from them. I also want to use them later to use as a form to add rows to this table.

So what do I do? How do I take these properties and make a collection of them?

public class UserViewModel()
{
    [Required()]
    public string UserName = {get; set;}
    [Required()]
    public string FirstName = {get; set;}
    [Required()]
    public string LastName = {get; set;}
}

I want to use these properties to generate my table and be used for a form.

The only thing I can think of is doing this

   public class AddUserViewModel()
    {
        [Required()]
        public string UserName = {get; set;}
        [Required()]
        public string FirstName = {get; set;}
        [Required()]
        public string LastName = {get; set;}
    }

   public class UserViewModel()
   {
       public List<User> Users {get; set;}
       public AddUserViewModel {get; set;}

       public UserViewModel()
       {
           Users = new List<Users>();
       }
   }

So basically I have it as a separate view model that is enclosed into another viewmodel that contains a list of Users(my domain model)

That way I use my domain model to generate the table and my AddUserViewModel for my adding of users.

Seems kinda redundant so I am not sure if there is a better way.

Edit

I have something like this

 var viewModel = new UserViewModel();
 List<Users> users=  UserService.GetAllUsers();
 viewModel = Mapper.Map<Users, UserViewModel>(users);
 return View("Index", viewModel);

I also tried

var viewModel = new UserViewModel();
 List<Users> users=  UserService.GetAllUsers();
 viewModel.AddUserViewModel = Mapper.Map<Users, AddUserViewModel>(users);
 return View("Index", viewModel);

Edit 2

I have this and it compiles but I get this error

        SomeViewModel viewModel = new SomeViewModel ();       
        List<User> users=  userService.GetAllUsers();
        viewModel.UserViewModel = Mapper.Map<List<User>, List<UserViewModel>>(users);
        return View("Index", viewModel);


Trying to map Domain.User to ViewModels.UserViewModel.
Missing type map configuration or unsupported mapping.
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.

Answer 1

Why would you want to return a list of domain objects in your view model? That's not what view models are supposed to be. View models should reference only other view models. So you have a nice UserViewModel which represents a user. Now you need to work with multiple users in your view, so either you pass an IEnumerable<UserViewModel> or if you need some other properties you design a view model for this:

public class UserViewModel
{
    [Required]
    public string UserName = { get; set; }
    [Required]
    public string FirstName = { get; set; }
    [Required]
    public string LastName = { get; set; }
}

public class SomeViewModel
{
    public List<UserViewModel> Users { get; set; }
    public string SomeOtherProperty { get; set; }
}

and now your controller action might look like this:

public ActionResult Foo()
{
    SomeModel model = _repository.GetModel();
    SomeViewModel viewModel = Mapper.Map<SomeModel, SomeViewModel>(model);
    return View(viewModel);
}

Now inside your view you could simply use a display template for this Users property (Html.DisplayFor(x => x.Users)) to show a list of them.

---

UPDATE:

After seeing your update here's how to proceed in terms of good practices:

public ActionResult Foo()
{
    IEnumerable<Users> users = _repository.GetUsers();
    IEnumerable<UserViewModel> usersViewModel = Mapper
        .Map<IEnumerable<Users>, IEnumerable<UserViewModel>>(users);
    return View(usersViewModel);
}

I've also used an AutoMap attribute in a sample project which could simplify your code to this:

[AutoMap(typeof(IEnumerable<Users>), typeof(IEnumerable<UserViewModel>))]
public ActionResult Foo()
{
    IEnumerable<Users> users = _repository.GetUsers();
    return View(users);
}

This attribute will automatically run after the controller action and before the view is rendered and would use AutoMapper to replace the model with the corresponding view model.