Here is what I'm trying to achieve.
I've got a ProjectBundle (Symfony2 bundle), with a Project Propel class. It represent an instance of a website, for example : two music band website share the code base, two different url, same logic but different data.
Various other Bundles (lets say "a dozen") can plug to the Project bundle, for example a BlogBundle will contain a Post and Comment Propel classes. A post is linked to a project via a foreign key (one project, several posts).
The issue is : the ProjectBundle is to remain independant, I don't want the Project class to have a Project::getPosts method because the BlogBundle might not be included in vendors.