仅在更新模型属性/列时处理事件 - Laravel Observer

Question

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 updated(\subject $subject) {
    info('After Update Event ' . $this->shouldUpdateThreads);
    if ($this->shouldUpdateThreads) {
        info_plus($subject);
    }
    info('After Update Check');
}

/**
 * Handling subject being updated event
 * Used to check if the teachers data has changed or not
 * @param \subject $subject
 */
public function updating(\subject $_subject) {

    $subject = \subject::find($_subject->id);

    $this->shouldUpdateThreads = ($subject->teacherId != $_subject->teacherId) ? true : false;

    info(($subject->teacherId != $_subject->teacherId));

    info("Thread update ? " . $this->shouldUpdateThreads);
}

public function deleted(\subject $subject) {
    info("Subject deleted");
}

}

这甚至是正确的方法吗？如果不是我做错了什么？

Answer 1

在 Eloquent 模型中，您可以getOriginal在更新属性时使用该方法。因此，如果您想获得原始值（更新前），teacherId您可以执行以下操作：

$subject->getOriginal('teacher_id');

见https://laravel.com/api/5.5/Illuminate/Database/Eloquent/Model.html#method_getOriginal

在您的代码中：

public function updated(\subject $subject) {
    info('After Update Event ' . $this->shouldUpdateThreads);
    if ($subject->getOriginal('teacher_id') !== $subject->teacher_id) {
        info_plus($subject);
    }
    info('After Update Check');
}