IoC Containers and Domain Driven Design

Question

I've been searching for guidance for using IoC containers in domain driven design. Evan's book unfortunately doesn't touch on the subject. The only substantial guidelines I could find on the internet is here.

Many of Malovic's points are common sense but I'm concerned about a few of them. He suggests that IoC container's should be reserved for resolving services only and that using an IoC container to resolve domain dependencies is a bad idea. However, he doesn't back up this assertion with any examples. He simple states it as a matter of fact.

He then goes on to say that mixing IoC containers and factories doesn't make sense. This appears to contradict his first point. If, in fact, domain dependencies shouldn't be resolved by an IoC container how then should they be resolved? Evan's book clearly points to factories as the logical choice.

I would appreciate any input you have on the matter. I'm a novice when it comes to both DDD and IoC. I'm struggling to grasp how IoC and DDD can work together.

Answer 1

In my opinion he is correct about not using IoC container in domain model. That practice I follow myself as well. Basic idea is that services may contain infrastructure dependencies and therefore its wise to mock them. Domain entities don't have those, so its not important to mock them up (still coding to interfaces is good practice).

Factories for domain entities should not be in IoC container, but factories for services should. Basically you may reference entity factories in your services. It's not very tight coupling.

Good reading about IoC can be found at Billy McCafferty's blog post "Dependency Injection 101"