map.resources :cars, :has_one => :driver
You're probably expecting to use form_for like this:
form_for([@car, @driver])
That won't work. It'll complain about not being able to find the function, 'car_drivers_path' instead of 'car_driver_path'
Fix:
form_for(@driver, :url => car_driver_path(@car))
Hopefully in Rails 2.1.1 this will be fixed using a different, less crazy syntax:
http://rails.lighthouseapp.com/projects/8994/tickets/461-fixed-polymorphic_url-to-be-able-to-handle-singleton-resources
That is all.
