Named route parameters should be more consistent

Hi everyone!

I’m writing concerning restful routes support using a custom parameter. For example,

resources :videos, param: :identifier

I think the feature is pretty awesome, but unfortunately I think it has a serious shortcoming. The great part is that requesting /videos/foobar will correctly call VideosController#show with a value of foobar in params[:identifier].

But the not so good part is that if you try and generate a route to a given video, the identifier attribute will be totally ignored and the id will be used instead.

v = Video.create(identifier: "foobar")
app.video_path(v) # This would return "/videos/1"

I know the current answer to this is to override to_param, but I think that’s not how it should be done. I opened a PR with more arguments behind my opinion, and a possible fix! I’d love to have some feedback :smile: