to_formatted_s

# File activesupport/lib/active_support/core_ext/array/conversions.rb, line 34
        def to_formatted_s(format = :default)
          case format
            when :db
              if respond_to?(:empty?) && self.empty?
                "null"
              else
                collect { |element| element.id }.join(",")
              end
            else
              to_default_s
          end
        end