I’m currently working on a project where I’m trying to make everything as extensible as possible. I have a Ticket model and I want everything to be ticketable (thats my polymorphic association).

The problem is that I want the URLs to be sensible and still have my polymorphic attribute loaded automatically without having to do to much hacking / un-dry code, so I wanted the URLs to be: /users/1/tickets/new.

This needs to be applied to any arbitrary number of models that has_many :tickets, :as => :ticketable .

The tickets controller needs to be able to get the object, and set it for a user to access it for the polymorphic form. instance_set_variable is the magic that lets this happen very easily. By having the before filter on create and new requests, the :get_object is called each request for those actions and the nested resources parent object is found and loaded into a variable called @ticketable .

The last bit of magic is the form_for that lets you create the ticket and have ticketable be automatically filled in by the rails engine with one little modification in the ticket_controllers.rb create method. Thats it!