Complex polymorphic routes

I've used polymorphic routes which seem to not be QUITE what most people mean when they use this term. Most discussions are intended to handle things like:

  /blogs/1/comments   /article/1/comments

where the comments controller handles different parent types.

I have often used something more like this:

  /users/1/domains   /domains

Each of these are "scoped" such that if a params[:user_id] is present, it will scope the domains list, via something like:

  def index     load_user     if @user       @domains = @user.domains     else       @domains = Domains.find :all     end   end

  private

  def load_user     if params[:user_id]       @user = User.find params[:user_id]     end   end

This technique works well for me, even if not QUITE so DRY as I would like. However, when the paths get more complicated:

  /users/1/domains/2/records/3   /domains/2/records/3   /records/3

my technique quickly becomes at best complicated, and at worse impossible to implement and debug easily. This is mainly because some operations are ALWAYS scoped (modifying a domain, for instance) while others are not. I suppose I could just check permissions on each operation and only scope the index method, as that is the only one I really want to narrow down data for. Once a user lists their domains, I don't care if it is used via the /domains/ prefix directly. However, this means that permission checking will have to occur, where by scoping it I manage to avoid having to do a lot of this, as all I need to do is check if curent_user.id == params[:user_id] or if current_user is an admin.

The additional scoping for direct operations on a specific item seem to be most of the problem, as it is mostly unnecessary.

Do others have solutions to this sort of problem that are cleaner than what I have done, or might end up doing?

Thanks, --Michael