Fetching data within an ASP.NET MVC ViewModel class?

Question

For those that create ViewModels (for use by typed views) in ASP.NET MVC, do you prefer to fetch the data from a service/repository from within the ViewModel, or the controller

Answer 1

Here's another solution: http://www.lostechies.com/blogs/jimmy_bogard/archive/2009/06/29/how-we-do-mvc-view-models.aspx

Main points there:

1. Mapping is done by a mediator - in this case it is AutoMapper but it can be your own class (though more to code). This keeps both Domain and ViewModel concentrated on the domain/presentation logic. The mediator (mapper) will contain (mostly automatic) logic for mapping, including injected services.
2. Mapping is applied automatically, all you do is tell the action filter the source/destination types - very clean.
3. (Seems to be important for you) AutoMapper supports nested mappings/types, so you can have your ViewModel combined of several independent view models, so that your "screen DTO" is not messy.

Like in this model:

public class WholeViewModel
{
   public Part1ViewModel ModelPart1 { get; set; }
   public Part2ViewModel ModelPart2 { get; set; }
}

you re-use mappings for specific parts of your View, and you don't write any new line of code, since there're already mappings for the partial view models.

If you don't want AutoMapper, you have have IViewModelMapper interfaces, and then your IoC container will help your action filter to find appropriate

container.Resolve(typeof(IViewModelMapper<>).MakeGenericType(mysourcetype, mydesttype))

and it will also provide any required external services to that mapper (this is possible with AutoMapper, too). But of course AutoMapper can do recursions and anyway, why write additional AutoMapper ;-)