Dependency Injection - use with Data Transfer Objects (DTOs)?

Question

Consider the code below (which has been simplified). I have a service class that returns a list of specific DTO objects that each implement their own specific interface. In

Answer 1

Have a look at AutoMapper. And I agree with @duffymo, I wouldn't use interfaces with DTO's. AutoMapper is a convention-based object to object mapper that will create and populate your DTO's for you. If nothing else it will save you a lot of typing. I've been through the exercise of writing conversion routines to/from DTO's with associated typos. I wish I had found AutoMapper a bit sooner. In the case of your example (where I've nominally made the "from" object of type Order):

public class Services : IServices
{    
    public IList<DTO> GetDTOs()
    {    
        ...
        Mapper.CreateMap<Order, DTO>(); // move map creation to startup routine
        var dtos = new List<DTO>();
        foreach (c in d) 
        {
            dtos.Add( Mapper.Map<Order, DTO>(c));
        }
        return dtos;
     }
}

Or using LINQ

public class Services : IServices
{    
    public IList<DTO> GetDTOs()
    {    
        ...
        Mapper.CreateMap<Order, DTO>(); // move map creation to startup routine
        return d.Select(c => Mapper.Map<Order, DTO>(c)).ToList();
     }
}

Answer 2

it doesn't make much sense to me to use any DI for DTOs. I would probably use the Factory Pattern to get DTOs for my model objects.

DTOs don't need their life cycle managed by the container; I would just new them. Dont over-engineer.

Answer 3

I don't think DTOs should implement interfaces, because they aren't likely to implement behavior that will change.

They also shouldn't be injected. Not all objects should be. I think this is an appropriate call to new: create the object, use it, let it go out of scope and be GC'd.