tp3 本身插入数据返回的就是它的主键id 值
eg:
$User = D("User"); // 实例化User对象
$data['username'] = $userinfo['nickname'];
$data['tel'] = $userinfo['province'];
$data['portrait'] = $userinfo['figureurl_qq_2'];
$data['time'] = time();
$insert = $User->add($data);
打印$insert 就是主键值