Comments on: Strengthening your domain: Encapsulated collections

By: Josh Kodroff

Josh Kodroff — Thu, 11 Nov 2010 17:29:07 +0000

This article really helped me pimp up my domain model. One thing, though…

I don’t get how you can have “private readonly IList _orders = new List();” and still do lazy loading (at least without adding extra variables to track whether you’ve tried to load the collection). What’s the solution for that?

By: bogardj

bogardj — Thu, 08 Apr 2010 12:21:42 +0000

@Rhys

Perhaps you can answer, why _would_ I do this? What does this extra code tax give me? Keep in mind I don’t care about anyone casting to IList or something else like that.

By: RhysC

RhysC — Thu, 08 Apr 2010 02:35:07 +0000

I dont want to harp on Jimmy, but why would you not just return an actual IEnum ?

public IEnumerable Orders {
get
{
foreach(var o in _orders)
yield return o;
}
}

Its a trival amount of additioonal code and gives you what you want. throw an extenion method to just make it return _orders.AsIEnumerable() and you are laughing

By: bogardj

bogardj — Fri, 02 Apr 2010 20:25:51 +0000

@Ryan

If there’s a screen to allow removing an order line, sure! The important thing here is to not expose the entire collection directly, but only the operations needed by the application.

By: Ryan Hartzog

Ryan Hartzog — Fri, 02 Apr 2010 19:51:38 +0000

I can see how the Customer Order relationship would not want to expose a RemoveOrder() method, but what about Order > OrderLine? In that instance the Order would publicly expose OrderLines() and RemoveOrderLine(OrderLine line) while keeping the AddOrderLine(OrderLine line) behavior internal?

By: Shane Courtrille

Shane Courtrille — Wed, 31 Mar 2010 18:34:51 +0000

Agreed with Markus. Udi had a good post on the idea that almost everything needs to come from something existing.

By: bogardj

bogardj — Tue, 23 Mar 2010 12:26:30 +0000

@Craig

Typically, we make the DTOs contain all writable members, including lists and collections. This is also what you’d need to do with serializable types, for example.

By: Craig

Craig — Mon, 22 Mar 2010 23:18:38 +0000

This might not be the place to ask this but I am wondering how you would configure AutoMapper to map the readonly IEnumerable to a DTO’s readonly IEnumerable? Or should the DTO just contain an IList or array?

By: Edin

Edin — Thu, 11 Mar 2010 17:16:04 +0000

@Jimmy

I wasn’t aware of this approach. Thanks a lot!

By: Markus Zywitza

Markus Zywitza — Thu, 11 Mar 2010 15:30:54 +0000

I’d rather object against the internal AddOrder() method than agaionst IEnumerable. IEnumerable is a clear hands-off sign for modifying.
But rather than have internal AddOrder, I would add
Order CreateOrder() {…}
to Customer. I know that this is slightly less testable, because I cannot stub the Customer for testing, but it is also cleaner. I remember a post from Udi Dahan that emphasizes this method of creating objects in a domain model.