[TYPO3-50-general] FLOW3 and DDD

[Robert Lemke]

Hi Xavier,

Am 19.01.2009 um 16:14 schrieb Xavier Perseguers:

>> You forgot to mention that in Nilsson example there is only "create
>> new", but create new Customer means create one with clear identity.
>> Without it: how can you add it to the repository when you don't  
>> know its
>> identity, how will you get it back? Therefore you first have to  
>> check if
>> one with that identity exists (via a repository).
>
> This sounds OK but do you mean that this is not repository's work to
> provide an ID/identity? I mean I do not need any identity (I  
> understand
> identity as the auto-increment field in a DB) to work with my  
> domain, I
> just need "pointers". That is when I "create" a new Customer. I have  
> to
> provide it's first name, last name and perhaps a business id if I need
> it but albeit from that, a new customer does not have any identity or
> business identity until it is persisted. I don't want to reserve a  
> free
> id (auto-incremented in MySQL) from the DBMS nor do I want to create a
> business id (thus not in relation with DB-stuff) until I do something
> useful for my business with this customer. That is for the business ID
> until it orders something for instance.

Correct, the Domain Model (usually) does not know about the technical
details of its identity.

Take a person: Each person is unique, for sure. But what identifier lies
in the domain of a Person? Surely no UUID. Usually you'd identify a  
person
by the combination of certain properties, such as last name, first name
and birth date.

The Person domain model doesn't know that the Content Repository is  
using
a UUID to identify the person. And it doesn't care when this happens.

In fact the identity of an Entity is managed by two authorities:

  - while it is transient, an entity is identified by its PHP object  
hash
  - as soon as it has been persisted, it is identified by its UUID

But that happens behind the scenes and with good reason ...

>> So, the example should read:
>> $customer = new Customer(12345); // where 12345 is the identity,
>> something like UUID
>> ($addressRepository->find(bla, blub);)
>> none found
>> $address = new Address(bla, blub); // again "bla/blub" is identity
>> $customer->setAdress($adress);
>> $customerRepository->add($customer);
>> $persistenceManager->persistAll();

I don't agree. You can create two Customers with exactly the same
properties which have separate identities:

$customerA = new Customer();
$customerB = new Customer();

Of course, in case of a customer it is wise to introduce some property
which makes identification (within the domain) easier, for example a
customer number.

But that customer number exists idenpendently from the object's UUID.

> That is you must generate an ID for all "new" customers regardless of
> whether they will be persisted later? I do not understand. If you
> generate a UUID, that's fine, it's unique by design but what if you  
> use
> a sequential business number?

exactly.

Cheers,
robert