[TYPO3-50-general] FLOW3 and DDD

[Nino Martincevic]

Hi Robert,

Robert Lemke schrieb:
> Yes, sure, but technically you can annotate a class as @entity, create
> an instance of it and don't add it to a repository or an entity which
> is part of an aggregate. Then it won't be persisted.
> 
> So conceptually a class annotated as @entity is always a member of an
> aggregate. But it doesn't mean that it will be persisted (that's only
> the case if it has a connectino to a repository).

Hm, that seems to be a conceptual problem, though I'm not aware of the 
whole current architecture and the next statement shows me that you have 
probably already thought of it.
You said:
"Therefore if you create an entity or value object, it will only be 
persisted if it is connected to an aggregate (an thus a repository)."

That's exactly the point.

I guess we agree that an entity is always part of an aggregate.
As you stated right (and a bit extended here) the only way to access an 
entity in DDD is through an aggregate (root) and an aggregate is only 
accessible through a repository.
So, there can't be any entity instance not "directed" (created or saved) 
by a repository. You simply cannot create an entity that belongs to an 
(complex) aggregate from outside without going through the root and 
therefore having a "connection", i.e. it has always a "connection" to 
the repository.

<Excursion>
Well actually not in DDD sense but in the current infrastructure and 
technical solution of Flow3. Because some DDD guys even don't do that 
with repositories, just maintaining the lifetime of living entities, 
keeping it completely peristance ignoring. A domain model should be that 
for being "perfect" but we also have to face the facts. And they are 
that there will be some persistence at some point.
But I'm with you regarding this issue, my repositories also "save"...
</Excursion>

On the other side perhaps you don't need to change anything. Because if 
someone wants to create an non-root entity bypassing the repository and 
aggregate he may do so for whatever reasons. But if he wants that entity 
to be persisted he has to add it to a aggregate/repository and he has to 
do it with the provided methods of the aggregate root.

Perhaps you could use an @aggregate annotation (if you don't have it 
already). That way you could avoid non-root entities to be created 
outside an aggregate, at least conceptually.

Maybe this thoughts could help to refactor the current implementation?
But like I already said: I don't want to impute that you haven't just 
thought of it...
:-)

>> And actually you don't and can't have a repository for value objects,
>> because they have no identity. How a repository would find them then?
> Sure, but I didn't say that, did I?

Well, don't know exactly ;-)
Perhaps I read this statement in the above citation...

Nino