Question

Introduction

I’m using ASP.Net MVC3. My Controllers talk to a service layer, and the service layer talks to a Data Acces layer which uses Entity Framework.
I get a specific entity using Entity Framework. This entity is converted into a DTO. Then I deliver this DTO to a MVC controller. Something like this:

pseudo code:

// This is inside my Service Layer
var entity = DataAccess.GetById(id);
var dto = createDtoWithValuesFrom(entity);
return dto; // Return dto to MVC controller

In this DTO I would like to use a dependency, to for example a Calculator. Let’s say my DTO looks like this:

public class Customer
{
  private ICalculator Calculator;

  public class Customer(ICalculator calculator)
  {
     Calculator = calculator;
  }

  public string Name { get; set; }
  public decimal Discount
  {
     get
     {
        return Calculator.Discount();
     }
  }
}

Problem

How do I instanciate my DTO, and let Autofac inject a calculator?
I can think of a way to do this:

var calculator = DependencyResolver.Current.GetService<ICalculator>;
var dto = new DTO(calculator );

But I don’t know if this is the best way to do it, since it smells of ServiceLocator, and I’ve read that it’s not prefered to use that.

Answer 1

DTOs normally have some properties and do not contain any logic.
You should consider a design where your MVC-Controller does something like this:

1. Get the customer from the service/dataaccess
2. Calculate the discount by invoking the ICalculator which could be passed to the Controller using constructor injection (or call an extra service which does the calculation)
3. Create a new model class which contains the customer and the calculated discount and pass this model to the view.

public class Model
{
  public Customer Customer { get; set; }

  public double Discount { get; set; }
}

public class SomeController : Controller
{
  private readonly DataAccess dataAccess;
  private readonly ICalculator calculator;

  public SomeController(DataAccess dataAccess, ICalculator calculator)
  {
    this.dataAccess = dataAccess;
    this.calculator = calculator;
  }

  public ActionResult Index(int id)
  {
    var model = new Model();
    model.Customer = this.dataAccess.Get(id);
    model.Discount = this.calculator.Calculate(customer);

    return View(model);
  }
}