Question

Many of my classes end up needing convert functions.

• DataRow -> Object converters
• ViewModel <-> Model Converters

My question is where should the functions live?

Option 1: Inside the source class

public class Employee
{
  public EmployeeViewModel ToViewModel() {}
}

var vm = myEmployee.ToViewModel()

Option 2: Inside the destination class

public class EmployeeViewModel
{
  public static EmployeeViewMOdel FromModel() {}
}

var vm = EmployeeViewModel.FromModel(myEmployee);

Option 3: Inside a converter

public class EmployeeModelViewModelConverter
{
  public static EmployeeViewModel ConvertToViewModel(Employee) {}
}
var vm = new EmployeeModelViewModelConverter.ConvertToViewModel(myEmployee);

---

Option 3 seems to be the cleanest at the cost of having tons of converter classes laying around and either tons of static functions or tons of initialization/IOC injection. It also has the ugliest syntax or you have to add yet another class using extensions.

Clarification: I’m not talking just about the ViewModel/Model classes, but anything where you need to convert one class to another. As another example, I have a rendering system where objects often need to be converted to renderable primitives.

Answer 1

I believe the Single Responsibility Principle suggests #3, its own converter class.

EDIT: If you need it in a separate method, then I’d hold to what I said above. But @kyoryu has a valid point about the ViewModel, however, I’d agree only if the Model is passed as an argument in the ViewModel constructor, not as a separate method.