TP的whereIn和设置提交参数默认值小技巧

$title = $this->request->post('title','');
或 
$title = input('title', 1);

快速查询关联的数据

$arr = model('LessonUser')->field('id,user_id,lesson_id')->where('lesson_id', $data['lesson_id'])->column('user_id');
$student = model('User')->field('id,nickname,mobile,avatar')->cache(true, 3600)->whereIn('id', $arr)->select();