def to_s(mode = :primary_code)
      res = send(mode) || primary_code
      res.respond_to?(:each) ? res.first.to_s : res.to_s
    end
def to_s(mode = :primary_code)
      res = send(mode) || primary_code
      res.respond_to?(:each) ? res.first.to_s : res.to_s
    end
String representation for the instance.
 @param mode [symbol] The attribute to for stringification
 @return [String]
 @api public