SDb::__get PHP Method

    public function __get($k)
    {
        if (isset($this->_fields->{$k})) {
            return $this->_fields->{$k};
        } else {
            //判断是不是属于外键
            foreach ($this->foreign_keys as $k2 => $v2) {
                $tmp = explode(".", $v2);
                if (!empty($tmp[0]) && !empty($tmp[1])) {
                    $tbl_name = trim($tmp[0]);
                    if ($k == $tbl_name) {
                        return $this->_fields->{$k} = new stdclass();
                    }
                }
            }
        }
        return null;
    }