Question

Situation: I have a large shrink wrapped application that my company bought. It is supposed to be extensible, yada, yada. It has a DB, DAL and BLL in the form of SQL and DLLs. It also has a MVC project (the extensible part) but 95% of the “Model” part is in the DAL/BLL libraries.

Problem: I need to extend one of the “Models” located in the BLL. It is an User object with 47 properties, 0 methods and no constructor. What I started was a simple deivation of their class like:

public class ExtendedUser : BLL.DTO.User
{
    public bool IsSeller { get; set; }
    public bool IsAdmin { get; set; }
}

This works fine if I just create a new ExtendedUser. However, it is populated by another call into their BLL like:

BLL.DTO.User targetUser = UserClient.GetUserByID(User.Identity.Name, id);

I tried the straight forward brute force attempt, which of course throws a Cast Exception:

ExtendedUser targetUser = (ExtendedUser)UserClient.GetUserByID(User.Identity.Name, id);

I am drawing a complete blank on this very simple OO concept. I don’t want to write a Constructor that accepts the existing User object then copies each of the properties into my extended object. I know there is a right way to do this. Can someone slap me upside the head and tell me the obvious?

TIA

Answer 1

If you do want to use inheritance, then with 47 properties, something like Automapper might help you copy all the values across – http://automapper.codeplex.com/ – this would allow you to use:

// setup
Mapper.CreateMap<BLL.DTO.User, ExtendedUser>();

// use
ExtendedUser extended = Mapper.Map<BLL.DTO.User, ExtendedUser>(user);

Alternatively, you might be better off using aggregation instead of inheritance – e.g.

public class AggregatedUser
{
    public bool IsSeller { get; set; }
    public bool IsAdmin { get; set; }
    public BLL.DTO.User User { get; set; }
}