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

[Shane Hathaway]

Just to be sure I understand, I think you meant to use the word 
"relationship" instead of "relation" throughout this message.

Max M wrote:
> If an object needs to be related to another object, there is no need for 
> any of the objects to know they are related. If all the relations are 
> external to the objects you can relate objects that are not programmed 
> to be related. Keeping all the relation code loosely coupled from the 
> objects.
> 
> Making the objects hold the responsibility for the relations means that 
> all objects has to take it into account. There is no reason for that. To 
> take a simplified example from Plone.
> 
> relations/
>   members_groups
> 
> Members/
> Groups/
> 
> In this case I can make the "members_groups" relationship manager take 
> care of the relations, and Members and Groups would not need to know 
> they can be related. I don't have to change the code in Members at all. 
> Thus leaving Plone as it is, while I can add group functionality.
> 
> maxm_groups = context.relations.member_groups.get(context.Members.maxm)
> 
> The other way around I would need to change the Member product, adding 
> group relations, and I can risk all hell breaking loose when Plone is 
> updated the next time.
> 
> I wonder if any of you guys reinventing relationships has even bothered 
> to try out the mxmRelations product? You are taking the long and winding 
> road to get to the same conclusions I did a year ago ...

I don't know about the others participating in this thread, but I'm 
reaching quite different conclusions than you did.  For example:

- The solution should not require Zope.

- It should not be necessary to visit the management interface to set up 
relationships.

- Developers should have the *option* of using relationships directly in 
their classes, with a Pythonic API.

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.

Shane