[TYPO3-mvc] Blog Example and Value Object question

[Jochen Rau]

Hi Franz.

Good reading! Thanks a lot.

Just a small remark: In the "books" a repository can only handle 
Entities and no ValueObjects. Although I set great store by consequently 
following the DDD paradigms, I would also allow ValueObjects.

Jochen

schrieb Franz Koch:
>> It's interesting that a concept leads to strict rules. I understand
>> now that a value object has no
>> intrinsic identity. Fine. But why on earth can't I ask for a list of
>> all existing value objects of a
>> certain kind? Because a book says so? ;)
>
> I think it's the terms used in DDD/objectPersistance that are misleading
> at the beginning, because they get interpreted in the wrong way by still
> having "traditional" concepts in mind.
> An identity of a object stands for the uniqueness of object, which
> doesn't mean that a object without a unique identity/personality doesn't
> have any identifier on database level. That's a thing I just learned.
>
> Maybe a example might help - and I hope I got this one right:
>
> Assume we have a valueObject "name" and a "person" object (which are not
> related to each other in this example), and both of them have the
> name/value "John Doe". Also assume the according repositories could
> contain several objects with this name/value.
>
> Now, if you ask the nameRepository to give you a valueObject back that
> has the value "John Doe", you actually don't care which one of the John
> Does you get back, because you only care for the correct value that any
> of those has. So they are interchangeable. But although they are
> interchangeable and have no necessary personality/"identity", you still
> can ask the repository to give you a list of all names.
>
> In opposit, if you ask the personRepository for a person named "John
> Doe" you most likely are looking for a specific person, maybe your
> friend. So you actually care which one of the John Does you get back -
> you're searching for a person with a certain personality, a specific
> identity. There is only one Martin Kutschker, only one Nathan Lenz and
> only one Franz Koch that are related to this posting. Although in the
> whole world(Repository) there might be more guys having the same names
> as we have, we're not interchangeable with them, because everybody could
> see that it's not us.
>
>
>
> Of course there might be situations where you might not care if you get
> a specific person but just need any person, and there might be
> situations where you're looking for a specific name written in a special
> font with rainbow colors. In those cases you would have to change the
> objectTypes accordingly. But this depends on the domain you're using
> these objects in. So there is no strict rule that a person has to be a
> entity.
>
> Hope that helps somebody - and I hope I got it right ;)

-- 
Every nit picked is a bug fixed