$db = Flight::db();是什么意思？

<?php
header("Content-type:text/html;charset=utf-8");
$detector_id = isset($_REQUEST['detector_id']) ? trim($_REQUEST['detector_id']) : 0;

$db = Flight::db();

$and = [];
$and['detector_id'] = $detector_id;
$and['del_status'] = 0;

$detector_info = $db->get('tb_detector','*',[
    'AND' => $and
]);

if(!$detector_info){
    echo_json('请确认终端信息',ERR_UNNO);
}
$model = $detector_info['model'];
?>

这一串代码大概什么意思？刚接触PHP不是很懂。在教程中学习PHP没有看到过，从哪里可以学习到？

这是PHP的Flight框架， https://github.com/baizhebz/flight-doc-cn/blob/master/flight.doc.cn.md https://github.com/baizhebz/flight-doc-cn/blob/master/flight.doc.cn.md

同上