Automapper Mapping IEnumerable<SelectListItem> for Dropdown Menu

Question

Problem

I am currently adding automapping to my MVC project and I am stuck. Right now I have a User model used to represent data in the database. I have to map that model to a EditUserModel which will be used when the Edit method is called. The EditUserModel has IEnumerable<SelectListItem> (for a dropdown menu) that I can't seem to figure out how to map.

Attempted Solution

As of right now I haven't tried to implement anything. I am unsure where the best place for the IEnumerable<SelectListItem> or where to populate it. Right now it is being populated in the Controller.

User.cs

public class User
{
    [Key]
    public int UserID { get; set; }

    public string Username { get; set; }

    public string Password { get; set; }

    public int RoleID { get; set; }

    [ForeignKey("RoleID")]
    public virtual Role Role { get; set; }
}

EditUserModel.cs

public class EditUserViewModel
{
    [HiddenInput(DisplayValue = false)]
    public int UserID { get; set; }

    [Required]
    public String Username { get; set; }

    [Required]
    [DataType(DataType.Password)]
    public string Password { get; set; }

    [DisplayName("Role")]
    [Required]
    public int RoleID { get; set; }

    //The trouble field
    public IEnumerable<SelectListItem> Roles { get; set; }
}

Controller.cs

EditUserViewModel model = new EditUserViewModel();
//Population of the dropdown menu
model.Roles = context.Roles
    .ToList()
    .Select(x => new SelectListItem
    {
        Text = x.Description,
        Value = x.RoleID.ToString()
    });
//Mapping that the automaper will take care of
model.UserID = user.UserID;
model.Username = user.Username;
model.RoleID = user.RoleID;

Answer 1

For the record, here is what I was talking about in the comments to Jakub's answer:

public static class EnumerableExtensions
{
    public static IEnumerable<SelectListItem> ToSelectList<T, TTextProperty, TValueProperty>(this IEnumerable<T> instance, Func<T, TTextProperty> text, Func<T, TValueProperty> value, Func<T, bool> selectedItem = null)
    {
        return instance.Select(t => new SelectListItem
        {
            Text = Convert.ToString(text(t)),
            Value = Convert.ToString(value(t)),
            Selected = selectedItem != null ? selectedItem(t) : false
        });
    }
}

Needless to say, this is dramatically simpler and accomplishes the same thing (and is actually more robust in the event that the property paths are non-simple, since Jakub's solution will not work with nested properties).

(This is not really an answer, I'm posting it as a community wiki just to help elaborate a point)

Answer 2

Controller is a perfect place to populate your view models.

You can remove plumbing code by using this extension method:

public static class EnumerableExtensions
{
    public static IEnumerable<SelectListItem> ToSelectList<T, TTextProperty, TValueProperty>(this IEnumerable<T> instance, Expression<Func<T, TTextProperty>> text, Expression<Func<T, TValueProperty>> value, Func<T, bool> selectedItem = null)
    {
        return instance.Select(t => new SelectListItem
        {
            Text = Convert.ToString(text.ToPropertyInfo().GetValue(t, null)),
            Value = Convert.ToString(value.ToPropertyInfo().GetValue(t, null)),
            Selected = selectedItem != null ? selectedItem(t) : false
        });
    }

    public static PropertyInfo ToPropertyInfo(this LambdaExpression expression)
    {
        MemberExpression body = expression.Body as MemberExpression;

        if (body != null)
        {
            PropertyInfo member = body.Member as PropertyInfo;
            if (member != null)
            {
                return member;
            }
        }

        throw new ArgumentException("Expression is not a Property");
    }
}

model.Roles = context.Roles.ToSelectList(r => r.RoleID, r => r.Description);