c# - MVC - Controller with multiple select lists

Question

Are there any good ways to keep my controllers simpler when they have models that depend on a lot of select lists? I try to keep most of my controller actions as simple as possible (hopefully no more than 10 or so lines) but on pages that require a lot of dropdowns my actions usually exceed this:

public class Model
{
    public IEnumerable<SelectListItem> AllLocations { get; set; }
    public IEnumerable<SelectListItem> TopLocations { get; set; }
    public IEnumerable<SelectListItem> AllTemplates { get; set; }
    public IEnumerable<SelectListItem> TopTemplates { get; set; }
    // ...
}

[HttpGet]
public ActionResult Index(int id)
{
    var domain = Repository.Get(id);
    var model = Mapper.Map<Domain, ViewModel>(item);

    // any way to abstract this type of code?
    model.AllLocations = new SelectList(repository.GetAllLocations(), "Value", "Text");
    model.TopLocations = new SelectList(repository.GetTopLocations(), "Value", "Text");
    model.AllTemplates = new SelectList(repository.GetAllTemplates(), "Value", "Text");
    model.TopTemplates = new SelectList(repository.GetTopTemplates(), "Value", "Text");
    // etc. etc.

    return View(model);
}

[HttpPost]
public ActionResult Index(ViewModel model)
{
    // any way to abstract this type of code?
    model.AllLocations = new SelectList(repository.GetAllLocations(), "Value", "Text");
    model.TopLocations = new SelectList(repository.GetTopLocations(), "Value", "Text");
    model.AllTemplates = new SelectList(repository.GetAllTemplates(), "Value", "Text");
    model.TopTemplates = new SelectList(repository.GetTopTemplates(), "Value", "Text");
    // etc. etc.

    return View(model);
}

Answer 1

As you say keeping controller actions small is great. As Jimmy Bogard says put your controllers on a diet!

I use an IModelEnricher combined with Automapper. I return an entity etc using a specific ActionResult that then automaps my entity to a ViewModel and enriches with data required for select lists (and any additional data required). This method keeps your code DRY and controllers thin like a super model :-)! Also keeping the select list data as part of your ViewModel keeps your controller, model, and view responsibilities clear.

Defining a ViewModel ernicher means that anywhere that ViewModel is used it can use the same enricher to get its properties. So you can return the ViewModel in multiple places and it will just get populated with the correct data.

In my case this looks something like this in the controller:

public virtual ActionResult Edit(int id)
{
    return AutoMappedEnrichedView<PersonEditModel>(_personRepository.Find(id));
}

[HttpPost]
public virtual ActionResult Edit(PersonEditModel person)
{
     if (ModelState.IsValid){
            //This is simplified (probably don't use Automapper to go VM-->Entity)
            var insertPerson = Mapper.Map<PersonEditModel , Person>(person);
            _personRepository.InsertOrUpdate(insertPerson);
            _requirementRepository.Save();
            return RedirectToAction(Actions.Index());
      }
     return EnrichedView(person);
 }

This sort of ViewModel:

public class PersonEditModel
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
    public int FavouriteTeam { get; set; }
    public IEnumerable<SelectListItem> Teams= new List<SelectListItem>();
}

With this sort of Enricher:

public  class PersonEditModelEnricher :
IModelEnricher<PersonEditModel>
{
    private readonly ISelectListService _selectListService;

    public PersonEditModelEnricher(ISelectListService selectListService)
    {
        _selectListService = selectListService;
    }

    public PersonEditModelEnrich(PersonEditModel model)
    {
        model.Teams = new SelectList(_selectListService.AllTeams(), "Value", "Text")
        return model;
    }
} 

One other option is to decorate the ViewModel with attributes that define how the data is located to populate the select list. Like:

  public class PersonEditModel
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int Age { get; set; }
        public int FavouriteTeam { get; set; }
        [LoadSelectListData("Teams")]
        public IEnumerable<SelectListItem> Teams= new List<SelectListItem>();
    }

Now you can decorate an appropriate method in your select service with an attribute like:

   [ProvideSelectData("Teams")]
   public IEnumerable Teams()
   {
        return _teamRepository.All.ToSelectList(a => a.Name, a => a.TeamId);
   }

Then for simple models with no complex enrichment just the generic enrichment process can handle it. If you want to do anything more complex you can define an enricher and it will be used if it exists.

See this question. Also this blog post and this. Also this question on Automapper forum