class ActiveRecord::Base

def self.object_id_attr(symbol, klass)
  module_eval %{
    def #{symbol}
      if @#{symbol}.nil? or (@old_#{symbol}_id != #{symbol}_id)
        @old_#{symbol}_id = #{symbol}_id
        klass = #{klass}.descendants.find { |d| d.#{symbol}_name == #{symbol}_id }
        klass ||= #{klass}
        @#{symbol} = klass.new
      else
        @#{symbol}
      end
    end
  }
end

def self.validates_path(*args)
  configuration = args.extract_options!
  validates_each(args, configuration) do |record, attr_name, value|
    page = Page.find_by_path(value)
    record.errors.add(attr_name, :page_not_found, default: configuration[:message]) if page.nil? || page.is_a?(FileNotFoundPage)
  end
end