MVC where should the logic go the Controller or the View Model

Question

I have an MVC app where I'm wanting to display a dropdownlist with info from the database.

The dropdown will display info from database Cars using the table Make which is the make of the car.

So in my view I will have something like:

@model VectorCheck.ViewModels.CarsViewModel ... @Html.DropDownListFor(modelItem => Model.MakeId, Model.Makes) ...

So somehow I need to get the view model the list of makes.

So I might have some logic to go with this say only cars that are colour Red.

var redCars = _unitOfWork.Cars(x => x.Colour == "Red");

So my question is where is the best practise to put the logic for this query. Should it go in the viewModel or controller.

The way I see it I have two Options.

Option 1: The controller.

public ActionResult Edit(int id) { var car = _unitOfWork.CarRepository.Get(id); var carMakes = _unitOfWork.CarMakeRepository.Where(x => x.Colour == "Red").Select(u => new SelectListItem { Value = u.CarMakeId.ToString(), Text = u.Name }); return View("Edit", new InsertUpdateCarViewModel(car, carMakes)); }

ViewModel

public Car Car { get; set; } public IEnumerable<SelectListItem> CarMakes { get; set; } InsertUpdateCarViewModel(Car car, IEnumerable<SelectListItem> carMakes) { Car= car; CarMakes = carMakes; }

So in this example I get the carMakes in the controller and give them to the viewModel which is simply a container.

Opon 2: The viewModel

public ActionResult Edit(int id) { var car = _unitOfWork.CarRepository.Get(id); return View("Edit", new InsertUpdateCarViewModel(car)); }

ViewModel

public Car Car { get; set; } public IEnumerable<SelectListItem> CarMakes { get; set; } InsertUpdateCarViewModel(Car car) { Car= car; CarMakes = _unitOfWork.CarMakeRepository.Where(x => x.Colour == "Red").Select(u => new SelectListItem { Value = u.CarMakeId.ToString(), Text = u.Name }); }

So in this option I'm putting the logic to get the correct carmakes in the view model. It is more than a container.

So what I'm wanting to know is which of these ways is the correct way of doing this?

Joel Purra · Accepted Answer · 2012-06-10 21:01:58Z

In the controller. The ViewModel should not be aware of the unit of work you are using. Also, the view model in this case would be a lot more reusable if it didn't have to rely on the logic x => x.Colour == "Red". Even though this could be moved to the arguments, in general, I believe your models (and therefor views) would be much more reusable taking care of that in the controller.

exception · Accepted Answer · 2012-06-10 21:07:35Z

As already answered, it is the controller. To make it more memorable for you, I would put it this way. Do not let your view talk to the database directly. View asks/talks to Controller ONLY. Then obviously it makes sense for the view to send a request to the controller which forwards it to the database. Hope this helps for future!

Dante · Accepted Answer · 2012-06-10 21:01:37Z

You should add your logic to the Controller. In MVC, the ViewModel is an object that contains properties used in your view, no business logic in there.

David Neale · Accepted Answer · 2012-06-10 21:04:02Z

Any answer would be very subjective but I'd suggest that having the _unitOfWork reference (or any dependancy which needs injecting) within your view model rather violent separation of concerns.

Keep it in the controller - far cleaner.

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