references

# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 518
      def references(*args)
        options = args.extract_options!
        polymorphic = options.delete(:polymorphic)
        args.each do |col|
          column("#{col}_id", :integer, options)
          column("#{col}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) unless polymorphic.nil?
        end
      end