ActiveRecord Reference Proxy (lazy-load)

active_record_reference.rb

require 'active_record'

module ActiveRecord

  #
  # @see http://stackoverflow.com/questions/28434966/lazy-load-activerecord-proxy-instance Lazy-load ActiveRecord proxy instance
  #
  class Reference < ActiveSupport::ProxyObject

    def initialize(record_class, primary_key)
      raise ArgumentError, "Illegal record type: #{record_class.class}" unless record_class.is_a? Class
      raise ArgumentError, "Not an ActiveRecord type: #{record_class}" unless record_class < ActiveRecord::Base
      raise ArgumentError, "No primary key given" unless primary_key.present?

      @type = record_class
      @id = primary_key
    end

    def __record__
      unless defined? @record
        @record = @type.find(@id)
      end
      @record
    end
    private :__record__

    def method_missing(name, *a, &b)
      if defined? @record
        @record.public_send(name, *a, &b)
      elsif name == :class
        @type
      elsif name.to_s == @type.primary_key
        @id
      else
        __record__.public_send(name, *a, &b)
      end
    end

    def respond_to_missing?(name, *a, &b)
      name == :class || name.to_s == @type.primary_key || __record__.respond_to?(name, *a, &b)
    end

  end

  #
  #   class User < ActiveRecord::Base; end
  #
  #   user = User.find(user_id)
  #   user = User.reference(user_id)
  #
  class Base

    def self.reference(primary_key)
      Reference.new(self.class, primary_key)
    end

  end

end