preprocess_order_args

# File activerecord/lib/active_record/relation/query_methods.rb, line 1170
    def preprocess_order_args(order_args)
      order_args.map! do |arg|
        klass.send(:sanitize_sql_for_order, arg)
      end
      order_args.flatten!
      validate_order_args(order_args)

      references = order_args.grep(String)
      references.map! { |arg| arg =~ /^([a-zA-Z]\w*)\.(\w+)/ && $1 }.compact!
      references!(references) if references.any?

      # if a symbol is given we prepend the quoted table name
      order_args.map! do |arg|
        case arg
        when Symbol
          arel_attribute(arg).asc
        when Hash
          arg.map { |field, dir|
            arel_attribute(field).send(dir.downcase)
          }
        else
          arg
        end
      end.flatten!
    end