[TYPO3-50-general] FLOW3 and DDD

[Nino Martincevic]

Are you interested in any further constructive and also critical comments?

Robert Lemke schrieb:
> Hi Nino,
> 
> Am 19.01.2009 um 11:51 schrieb Nino Martincevic:
> 
>>> 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.
> 
> There can be Domain Objects without connection to the repository which  
> are then
> not persisted. I call them "Transient Entities".
> 
> Do you've got a copy of Jimmy Nilsson's "Applying Domain-Driven Design
> and Patterns"? Check out p. 281, the table which gives a summary of
> the Semantics for the Life Cycle of Domain Model instances.
> 
> $customer = new Customer;            // $customer is a Transient Entity
> $customerRepository->add($customer); // $customer added to the  
> repository
> $persistenceManager->persistAll();   // $customer becomes a Persisted  
> Entity
> 
> $address = new Address;              // $address is transient
> $customer->setAddress($address);     // $address now has connection to a
>                                          repository through the  
> Customer Aggregate
> 
> $persistenceManager->persistAll();   // $address will be persisted
> 
>> <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>
> 
> The Domain Model is completely Persistence Ignorant. We weave in some
> persistence code through AOP.
> 
>> 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.
> 
> Yes, for example you'll want to create a Customer object without  
> persisting
> it until it's valid. Imagine a multi step form which carries a  
> Customer in
> a session until the form is finally submitted.
> 
>> 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.
> 
> In fact there is nothing such an Aggregate object or Aggregat Root  
> object
> in FLOW3. Aggregates merely exist as a concept.
> 
> In the above example we have a Customer Repository and the Customer  
> entity
> automatically serves as an aggregate root. Address is part of the  
> Customer
> aggregate (in that example at least).
> 
>> 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.
> 
> See above - there's no Aggregat class / object.
> 
> Cheers,
> robert
> 
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