delegation.rb

# this is an experiment that I tried about 3 years ago.
# instead of calling asset.attachable.post.user.login just calling asset.login
 
class User <  ActiveRecord::Base #fields are :login, :email
  has_many :posts
  has_many :channels
end

class Channel <  ActiveRecord::Base #fields are :private(bool), :channel_type, :name
  belongs_to :user
  has_many :posts
end

class Post <  ActiveRecord::Base #fields are :title, :body, :comments_count
  belongs_to :user
  belongs_to :channel
  has_many :assets, :as => :attachable
end

class Asset < ActiveRecord::Base
  belongs_to :attachable, :polymorphic => true
  include AssociationDelegation
  set_delegation_chain :attachable, :channel, :user
end

require 'active_support'
module AssociationDelegation
  
  def self.included(base)
    base.send :cattr_accessor, :class_delegation_chain
    base.extend ClassMethods
    
    def method_missing(method_name, *args, &block)
      super(method_name, *args, &block)
      rescue NoMethodError => error
        puts "the error is #{error}"
        if delegated = self.find_delegated(method_name)
          return delegated.send(method_name, *args, &block)
        end
        raise error
    end

    def find_delegated(method)
      self.class_delegation_chain.inject(self) do |cur, association|
        cur = find_next_in_chain_or_start_new_chain(cur, association)
        return cur if cur.respond_to? method
        cur
      end
      return nil
    end
    
    def find_next_in_chain_or_start_new_chain(cur, association)
      return cur.send(association) if cur.respond_to?(association)
      return self.send(association) if self.respond_to?(association)
      nil
    end
    
  end
  
  module ClassMethods
    def set_delegation_chain(*classes)
      self.class_delegation_chain = [*classes]
    end
  end
end