Resource A and B are nested. In the form for C, I need to populate a dropdown of B:s depending on the value of A.
Trying to be RESTful, my approach is to have an onchange-handler on the A dropdown which calls the index action of B and redraws the B dropdown using RJS and a partial.
My concern is that because the RJS and partial should generate a select-helper for editing C, the code in the "B domain" (controller, RJS, partial) needs to be C-aware which feels ugly...
Does anybody have an alternative design which makes this cleaner somehow?
Another (perhaps silly) question. If I use the form builder object in the partial for B, it seems hard to reuse it from RJS because I don't have a form builder object there. Or should I skip the form builder for the B dropdown and use the instance variable instead? (Similar to how scaffolding in earlier version of Rails did it)
Wow, that's a long and somewhat strange post. I'm impressed that you
made it to the end! 
