Laravel model relationships and model events

Question

I am building a notification system at the moment, and the notifications get delivered via model events. Some of the notifications are dependent on things happening with the models relationships.

Example: I have a project model that has a one:many relationship with users,

public function projectmanager() {
    return $this->belongsToMany('User', 'project_managers');
}

I am wanting to monitor for changes on this relationship in my project model events. At the moment, I am doing this by doing this following,

$dirtyAttributes = $project->getDirty();
foreach($dirtyAttributes as $attribute => $value) {
   //Do something
}

这是在::updating模型事件中运行，但只查看模型属性而不是任何关系数据，是否可以获取旧关系数据和新关系数据进行比较和处理？

Answer 1

您应该为此使用观察者类。

这个 SO answer已经相当简单和很好地涵盖了这一点，尽管该答案使用了一个稍微旧的方法，其中类本身需要调用其观察者。当前版本的文档（本答案为 5.3）建议在您的应用程序服务提供者中注册观察者，在您的示例中，它类似于：

<?php
namespace App\Providers;

use App\Project;
use App\Observers\ProjectObserver;
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        Project::observe(ProjectObserver::class);
    }
}

为了评估新模型值与仍在关系数据库中的旧值之间的差异，Laravel 提供了以下方法：getDirty()和getOriginal()。

所以你的观察者看起来像：

<?php

namespace App\Observers;

use App\Project;

class ProjectObserver
{
    /**
     * Listen to the Project updating event.
     *
     * @param  Project $project
     * @return void
     */
    public function updating(Project $project)
    {
        $dirtyAttributes = $project->getDirty();
        $originalAttributes = $project->getOriginal();
        // loop over one and compare/process against the other
        foreach ($dirtyAttributes as $attribute => $value) {
            // do something with the equivalent entry in $originalAttributes
        }
    }
}