I am a bit new to DDD and bear with me if my understanding seems way off.
My question is about Udi's solution to domain events, particularly the class DomainEvents
(see code below)
An excerpt from Udi's code. It lives domain model as a static class.
public static class DomainEvents
{
[ThreadStatic] //so that each thread has its own callbacks
private static List<Delegate> actions;
public static IContainer Container { get; set; } //as before
//Registers a callback for the given domain event
public static void Register<T>(Action<T> callback) where T : IDomainEvent
{
if (actions == null)
actions = new List<Delegate>();
actions.Add(callback);
}
//Clears callbacks passed to Register on the current thread
public static void ClearCallbacks ()
{
actions = null;
}
//Raises the given domain event
public static void Raise<T>(T args) where T : IDomainEvent
{
if (Container != null)
foreach(var handler in Container.ResolveAll<Handles<T>>())
handler.Handle(args);
if (actions != null)
foreach (var action in actions)
if (action is Action<T>)
((Action<T>)action)(args);
}
}
Based on the code above, in order for the DomainEvents
to be used by the domain model, both must first be in the same assembly. Which makes the DomainEvents
part of the domain model right? (I may be wrong here)
So my question is: Does DomainEvents
itself breaks the rule "ubiquitous language of DDD"? Because it's implementation does not pertain to any domain.
My other concern is that the static member IContainer
creates an ioc-container-dependency in the domain model. Though I am not really sure if Udi's IContainer
is an interface or an actual IoC container.
My 2nd question is: What is this IContainer
in the DomainEvents
class? If it is truly an IoC container then doesn't it break the rule of "DDD should not have an infrastructure in the domain"? Is my understanding correct that an IoC-Container is considered an infrastructure? (Please correct me if I'm wrong)
If you may find any of this confusing, please say so.
EDIT:
I have built my projects where the domain model is separated on its own assembly (I call this business layer) with absolutely no references to any infrastructure components. See onion architecture.
Now I want to incorporate the domain events pattern. But doing so forces me to add infrastructure components to my business layer. Components being the DomainEvents
and an IoC framework just to satisfy the IContainer
, both having no relation to the domain whatsoever.
Isn't one of the idea of DDD is about separating the infrastructure from the domain?
Now I will play the pragmatic programmer, I just wanted to know that is it generally ok to do so? are there alternatives? What are you thoughts on this approach? Am I missing something basic here?