[Zope] ZODB and Reportlab

Hi: I need to report my all "CDClass" in one pdf document. For do that i want to use the reportlab libs, but i don't know how i can access to my all "CDClass" with a External Method. I have a solution but i think that isn't the best: list all "CDCLass" with a DTMLmethod and pass that list to the my ExternalMethod. My question is: what is the best way for doing that task? Thanks Very Much in advance Have a nice day. JoRgE