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

[Max M]

Shane Hathaway wrote:

> 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 is implemented as a Zope product, but the base class that implements 
the relationships is actually pure Python. The latest version is based 
on an OOBTree to handle the relations.

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


No.

> - 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 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.

Here is a not even half baked pseudo example on how it could be 
implemented. Which uses the same idea as mxmRelations:

class ManyToMany: # simillar to a mxmRelations class

    "A many to many Relationships, it can also hold meta data attrs"

    def __init__(self, name):
        self.name = name
        self.__relationship_graph = {}
        
    def relate(self, obj1, obj2):
        "relates 2 objects"
        
    def unrelate(self, obj1, obj2):
        "unrelates 2 objects"
        
    def del(self, obj):
        "Delete all relations to and from obj"
        
    def get(self, obj):
        "returns all relations to object"



class RelationshipsManager:

    "Folder-like class to hold Relationships instances"

    def addRelationsships(self, name, relationsshipsInstance):
        "Adds a Relationships"

    def getRelationsships(self, name):
        "retuns a Relationships by name"

    def delRelationsships(self, name):
        "Delete a relationships"



    # 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]