Say I have resource comment that belongs to resources post and blog. I know that to nest comment into say, post would look like this:
map.resources :posts do |post| post.resources :comments end
However, if I wanted :comments to also belong to :blogs, how would I do that?
What you're really looking for is called Polymorphic Associations: http://wiki.rubyonrails.org/rails/pages/UnderstandingPolymorphicAssociations
Thanks a bunch! 
Actually I just read through that and while it's useful, I still want to know the syntax for defining such relationships.