public function add($field_list)
    {
        if (!is_array($field_list)) return false;

        foreach ($field_list as $value) {
            $field = new Query_Field();
            if (count($value) == 1) {
                $field->name              = $value;
                $this->field_list[$value] = $field;
                continue;
            }

            $field->name     = $value['name'];
            $field->function = $value['function'];

        }

        return true;
    }