Access the 'parent' resource from a nested one?

Is there a possibility in an action to get the parent controller for
which the nested resource is called? for instance if I have the
following in my routes.rb:

  map.resources :user do |users|
    users.resources :logos
  end

  map.resources :pic do |pics|
    pics.resources :logos
  end

How easy would it be to get the parent? for instance I could call the
following 2 URLs:
http://localhost:3000/pics/#{pic_id}/logos/#{logo_id} and
http://localhost:3000/users/#{user_id}/logos/#{logo_id}

Can I know which parent I am currently in?

Further explanations follows:

The logo class is a polymorphic class defined as follow:

class Pic < ActiveRecord::Base
   has_one :logo, :as => :logoable
end

class User < ActiveRecord::Base
   has_one :logo, :as => :logoable
end

class Logo < FlexImage::Model
  belongs_to :logoable, :polymorphic => true
end

Now in my logo controller, I want to show the correct logo for the
correct parent controller. The URL would look something like:

http://localhost:3000/pics/#{pic_id}/logos/#{size}

Or

http://localhost:3000/users/#{user_id}/logos/#{size}

in my show action in the logo controller I have something like:

logo = Logo.find(:first, :conditions => {:logoable_type
=> ..., :logoable_id => ...})

logoable_type is either User or Pic. However, I can not see how to get
that value easily. I could play around with the param hash as it will
return either pic_id or user_id. Is there any simpler way to know
which parent the nested ressource is called from?

The above to follow DRY. Is there a way to map back from the action to
the parent controller?

I probably need a bit of REST vocabulary but hopefully it is clear
enough.

Regards,
Carl

I don't see what would be simpler than using pic_id or user_id (maybe
there is something?). From those you can generate any kind of setup
you want, just put in a before_filter so it's available to all
actions. Or do something like:

private
def pic?
  !params[:pic_id].blank?
end

Not sure if there's anything built-in, but I don't see the need for it.

Carl,

You can find an approach you can use discussed here
http://revolutiononrails.blogspot.com/2007/05/drying-up-polymorphic-controllers.html

Regards,
Val

Val,

Thanks for the post, that looks to be exactly what I am looking for. I
will leave any comments if any on the article.

Regards,
Carl