我在这里处理模型的两个事件，更新和更新，如下面的代码所示。我担心的是，只有在teacherId 已更改的情况下，我才想在更新的事件中执行某些任务，因此我想检查更新事件中的值并使用类属性来了解它是否已更改，但该标志假设其定义的值总是返回 false。
namespace App\Observers;
class SubjectObserver {
private $shouldUpdateThreads = false;
/**
* Listen to the ThreadList created event.
* This events Fire when ThreadList is handled
* @param \App\Observers\App\ThreadList $threadList
*/
public function created(\subject $subject) {
}
/**
* Listen to the ThreadList saved event.
* @param \App\Observers\App\ThreadList $threadList
*/
public function saved(\subject $subject) {
}
/**
* Handling subject updated event
* Used to update the threads and related models
* @param \subject $subject
*/
public function …