[Zope-dev] RFC: RelationAware class for relations betweenobjects

[Shane Hathaway]

Max M wrote:
>> - Developers should have the *option* of using relationships directly 
>> in their classes, with a Pythonic API. 
> 
> I think that should be working on top a general relationship service.

I agree.  It would be helpful, though, to identify a use case that 
describes why both you and I believe that relationships must be stored 
in a centralized location.  I'd like this to justify a particular 
implementation I'm considering (see below.)

>> I listed other requirements this morning, and as far as I can tell, 
>> few are fulfilled by mxmRelations.  On the other hand, maybe I 
>> misunderstand mxmRelations.  Does it fulfill the requirements I 
>> listed?  I'm sure there's nothing wrong with mxmRelations, but it 
>> seems like we're targetting different audiences. 
> 
> Let me say that I am not married to mxmRelations, and I am not trying to 
> push it as a solution. But I think it has a sound model for 
> relationships. One that is very general and expandable.

Ok, I'll take a look.

>    # perhaps a method on ZODB to return the RelationshipsManager ?
>    rm = ZODB().getRelationshipsManager()
>       rm.addRelationsships('members_groups', ManyToMany('members_groups'))
>    r = rm.getRelationsships('members_groups')
>    r.relate(someNewMember, someGroup)
>    groups = r.get(someMember)
>       >>> [someGroup]

We shouldn't add a getRelationshipsManager() method to any ZODB classes. 
  In pure-ZODB mode, a possible way to store relationships is the use of 
a special branch of the ZODB root object.  In Zope, there are normally 
two branches of the root object, "Application" and "ZGlobals". 
Relationship management could use a private branch, perhaps called 
"Relationships".  But the application should not have to know that at 
all; it should never access self._p_jar.root()['Relationships'].  That 
should be abstracted away.

Shane