Question

So lets say I have two models:
Thingy and Status. Thingy has a Status, and Status has many Thingies. It’s typical “Object and Object type relationship”.

I have a view where I just want the number of thingies in each status. Or basically a list of Status.Name and Status.Thingies.Count. I could do exactly this, but is the “right” thing to do to create a view model in the form:

ThingiesByStatusViewModel
-StatusName
-StatusThingiesCount

and hook it up with something like AutoMapper.

For such a trivial example, it probably doesn’t make much of a difference, but it would help me understand better the proper ‘separation of concerns’.

Answer 1

Should I use a viewmodel here?

Is this a rhetorical question?

Your view model would look exactly as you propose and it is perfectly adapted to what you are trying to display here:

public class ThingiesByStatusViewModel
{
    public string StatusName { get; set; }
    public int StatusThingiesCount { get; set; }
}

and then your controller would return an IEnumerable<ThingiesByStatusViewModel>. Then in your view you could simply use a display template:

@Html.DisplayForModel()

and the corresponding display template (~/Views/Shared/DisplayTemplates/ThingiesByStatusViewModel.cshtml):

@model AppName.Models.ThingiesByStatusViewModel
<div>
    <span>StatusName: @Model.StatusName</span>
    <span>Number of thingies: @Model.StatusThingiesCount</span>
</div>

Now let’s look at the mapping layer. Suppose that we have the following domain:

public class Thingy
{ }

public class Status
{
    public string StatusName { get; set; }
    public IEnumerable<Thingy> Thingies { get; set; }
}

and we have an instance of IEnumerable<Status>.

The mapping definition could look like this:

Mapper
    .CreateMap<Status, ThingiesByStatusViewModel>()
    .ForMember(
        dest => dest.StatusThingiesCount,
        opt => opt.MapFrom(src => src.Thingies.Count())
    );

and finally the controller action would simply be:

public ActionResult Foo()
{
    IEnumerable<Status> statuses = _repository.GetStatuses();
    IEnumerable<ThingiesByStatusViewModel> statusesVM = Mapper.Map<IEnumerable<Status>, IEnumerable<ThingiesByStatusViewModel>>(statuses);
    return View(statusesVM);
}