keywordable.rb

module Keywordable
  module ClassMethods
    def keyword(symbol, proc)
      write_inheritable_attribute :keywords, {} unless read_inheritable_attribute :keywords
      read_inheritable_attribute(:keywords)[symbol] = proc
    end
  end
  
  module InstanceMethods
    def keywords
      self.class.read_inheritable_attribute(:keywords)
    end
    
    def to_keywords
      returning({}) do |h|
        keywords.each do |keyword, proc|
          h[keyword] = proc.call(self)
        end
      end
    end
  end
  
  def self.included(receiver)
    receiver.extend         ClassMethods
    receiver.send :include, InstanceMethods
  end
end

# class Program < ActiveRecord::Base
#  include Keywordable
#  
#  belongs_to :city, :include => :county
#   
#  keyword :city, Proc.new { |program| program.city.name }
#  keyword :county, Proc.new { |program| program.city.county.name }
# end

# Program.first.to_keywords
# => {:city=>"ANSE BERTRAND", :county=>"GUADELOUPE"}