[Grok-dev] Having objects appear in more than one place in the Application Hierarchy

[Kevin Teague]

For modeling relationships such as "Courses have many Lessons and  
Lessons can belong to many Courses" (has and belongs to many) you may  
want to take a look at zc.relationship:

http://pypi.python.org/pypi/zc.relationship/

Note that the overview says, "It is expected to be used primarily as  
an engine for more specialized and constrained tools and APIs." so  
your head may explode a little bit upon reading the documentation for  
the pacakge ...

There are packages for Plone that builds upon zc.relationship to  
provide a more user-friendly API - something such as a  
megrok.relations package might be nice.

http://pypi.python.org/pypi/plone.relations

http://pypi.python.org/pypi/plone.app.relations

http://dev.comlounge.net/conference/plone-conference-2007-video-alec-mitchell-about-ploneapprelations-relationships-in-plone/