Domain Driven Design and IoC/Dependency Injection

Question

I\'m trying to apply now what I learned about DDD and I\'m a little bit confused about the flow of dependencies in the Domain model.

My questions are:

1. Shou

Answer 1

Should an Entity be aware of Factories, Repositories, Services in the domain?

• Application services: no
• Domain services: yes, because they are in the domain layer
• Factories: yes, because they are in the domain layer
• Repository interfaces: yes, because they are in the domain layer
• Repository implementations: no, because they are in the infrastructure layer

Notice the differente between interface and implementation: that's why you should use interface & implementations.

And FYI, Factories and Repositories are services after all, so you can generalize:

• Service interfaces: yes if they are in the domain layer

Easy

A domain service is one which is defined within the domain layer, though the implementation may be part of the infrastructure layer. A repository is a domain service whose implementation is indeed in the infrastructure layer, while a factory is also a domain service whose implementation is generally within the domain layer.

(Source: http://www.methodsandtools.com/archive/archive.php?id=97p2)

Should a Repository be aware of Services in the domain?

Usually no, why would it after all? The repository manage persistence. But I don't think that's "prohibited" because the infrastructure layer (persistence) knows about the domain layer.

Another thing that is bothering my mind is how to treat to collections when I want to add and entity to the collection.

Prefer the OOP approach when possible:

$article = new Article();
$article->addTag($tag);
$articleRepository->save($article);

I makes way more sense.

a domain service is any business logic that does not easily live within an entity.

(http://www.methodsandtools.com/archive/archive.php?id=97p2)

or also:

When a significant process or transformation in the domain is not a natural responsibility of an ENTITY or VALUE OBJECT, add an operation to the model as a standalone interface declared as a SERVICE.

(Eric Evans)

To sum up, create a domain service if you feel you need to, this is not automatic.