association extensions - has_one

Hi,

I'm struggling with something that must be very common pattern, and want to do it the correct rails/ruby way but am a bit dense !

I have users - an admin user, registered users and a guest user (using ModelSecurity)

For many of linked associations I want the admin to be able to list or edit all instances, the registered user only their own one and guest none at all.

So somehow I want to over ride or extend the associations, or find, so that the condition is captured in one place and my controller/view code isn't littered with these same if, else blocks...e.g something like...

       if(User.current.admin?)           Theme.find(:all)         elsif(User.current.registered?)           User.current.theme         else           nil         end

I've tried using the Association extensions so I can simply call something like

@theme = User.current.theme.find_theme

e.g

class User < ActiveRecord::Base

  has_one :theme do     def find_theme()        if(admin?)           Theme.find(:all)         elsif(registered?)           User.current.theme         else                    end     end   end

But no joy, this gives method missing. If I change the association to has_many however, it does work - but this is obviously not then correct with the model.

Do extensions only work for has_many ?

Any advice on best place or pattern to encapsulate this kind of situation much appreciated.

Many thanks tom