decorator.rb

module Decorators

  class Base < BasicObject
    # perhaps make this include ActiveModel and behave like the underlying ActiveRecord

    attr_reader :decorated

    def initialize(decorated)
      @decorated = decorated
    end

    def method_missing(method, *args)
      args.empty? ? decorated.send(method) : decorated.send(method, args)
    end
  end

  module Api
    
    class User < Decorators::Base
      def attributes=(attrs)
        # filter out disallowed attributes
      end
      
      def as_json
        { :id => decorated.id }
      end
    end
    
  end

   
end

user = User.find(123)
@user = Decorators::Api::User.new(user)