Laravel/Lumen事件传播控制：停止监听器执行的策略与实践

// app/Providers/EventServiceProvider.php
protected $listen = [
    App\Events\RegisterUserEvent::class => [
        App\Listeners\StoreUserListener::class,
        App\Listeners\SendVerificationEmailListener::class,
    ],
];

// app/Listeners/StoreUserListener.php
namespace App\Listeners;

use App\Events\RegisterUserEvent;
use App\Models\User;
use Exception;
use Illuminate\Contracts\Queue\ShouldQueue; // 如果是队列事件，请注意后续说明

class StoreUserListener // implements ShouldQueue // 如果是队列事件
{
    public function handle(RegisterUserEvent $event): bool
    {
        try {
            // 模拟用户已存在或存储失败的场景
            if ($event->email === 'existing@example.com') {
                throw new Exception("User with email {$event->email} already exists.");
            }

            $user = User::create([
                'name' => $event->name,
                'email' => $event->email,
                'password' => bcrypt($event->password),
            ]);

            if (!$user) {
                throw new Exception("Error saving user {$event->email}.");
            }

            // 存储成功，返回 true 或不返回任何内容 (默认返回 void)
            // 如果需要明确指示继续传播，可以返回 true
            return true; 

        } catch (Exception $e) {
            // 存储失败，记录错误并返回 false，以停止事件传播
            \Log::error("Failed to store user: " . $e->getMessage(), ['email' => $event->email]);
            return false; // 关键：停止传播
        }
    }
}

// app/Listeners/SendVerificationEmailListener.php
namespace App\Listeners;

use App\Events\RegisterUserEvent;
use Illuminate\Contracts\Queue\ShouldQueue; // 如果是队列事件，请注意后续说明
use Illuminate\Support\Facades\Mail;

class SendVerificationEmailListener // implements ShouldQueue // 如果是队列事件
{
    public function handle(RegisterUserEvent $event)
    {
        // 只有当 StoreUserListener 成功且没有返回 false 时，此方法才会被调用
        \Log::info("Attempting to send verification email to " . $event->email);
        // Mail::to($event->email)->send(new UserVerificationMail($event->user));
        // 模拟发送邮件
        dump('Verification email sent to ' . $event->email);
    }
}

// 在控制器或服务中
event(new App\Events\RegisterUserEvent('John Doe', 'test@example.com', 'password'));
// 如果 'test@example.com' 成功存储，则会发送邮件。
// 如果 'existing@example.com' 导致 StoreUserListener 返回 false，则不会发送邮件。
event(new App\Events\RegisterUserEvent('Jane Doe', 'existing@example.com', 'password')); 

// app/Providers/EventServiceProvider.php
protected $listen = [
    App\Events\RegisterUserEvent::class => [
        App\Listeners\StoreUserListener::class,
    ],
    App\Events\UserRegisteredEvent::class => [ // 新事件
        App\Listeners\SendVerificationEmailListener::class,
    ],
];

// app/Listeners/StoreUserListener.php
namespace App\Listeners;

use App\Events\RegisterUserEvent;
use App\Events\UserRegisteredEvent; // 引入新事件
use App\Models\User;
use Exception;
use Illuminate\Contracts\Queue\ShouldQueue;

class StoreUserListener implements ShouldQueue // 标记为队列监听器
{
    public function handle(RegisterUserEvent $event)
    {
        try {
            // 模拟用户已存在或存储失败的场景
            if ($event->email === 'existing@example.com') {
                throw new Exception("User with email {$event->email} already exists.");
            }

            $user = User::create([
                'name' => $event->name,
                'email' => $event->email,
                'password' => bcrypt($event->password),
            ]);

            if (!$user) {
                throw new Exception("Error saving user {$event->email}.");
            }

            // 存储成功后，调度新的事件
            event(new UserRegisteredEvent($user)); // 传递已创建的用户实例

        } catch (Exception $e) {
            \Log::error("Failed to store user (queued listener): " . $e->getMessage(), ['email' => $event->email]);
            // 失败时，不调度 UserRegisteredEvent，因此 SendVerificationEmailListener 不会被触发
            // 注意：这里不再返回 false，因为对队列监听器无效
        }
    }
}

// app/Listeners/SendVerificationEmailListener.php
namespace App\Listeners;

use App\Events\UserRegisteredEvent; // 监听新事件
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Support\Facades\Mail;

class SendVerificationEmailListener implements ShouldQueue // 标记为队列监听器
{
    public function handle(UserRegisteredEvent $event) // 接收 UserRegisteredEvent
    {
        \Log::info("Attempting to send verification email to " . $event->user->email);
        // Mail::to($event->user->email)->send(new UserVerificationMail($event->user));
        dump('Verification email sent to ' . $event->user->email);
    }
}

// 假设 RegisterUserEvent 有一个 public $user 或 public $status 属性
class RegisterUserEvent
{
    public $name;
    public $email;
    public $password;
    public $user = null; // 用于存储已创建的用户实例
    public $success = false; // 用于标记前一个操作是否成功

    public function __construct(string $name, string $email, string $password)
    {
        $this->name = $name;
        $this->email = $email;
        $this->password = $password;
    }
}

// StoreUserListener
class StoreUserListener implements ShouldQueue
{
    public function handle(RegisterUserEvent $event)
    {
        try {
            // ... 用户创建逻辑 ...
            $user = User::create([...]);
            $event->user = $user; // 将用户实例附加到事件对象
            $event->success = true; // 标记成功
        } catch (Exception $e) {
            $event->success = false; // 标记失败
        }
    }
}

// SendVerificationEmailListener
class SendVerificationEmailListener implements ShouldQueue
{
    public function handle(RegisterUserEvent $event)
    {
        // 在队列监听器中，此处的 $event 实例可能与 StoreUserListener 中的不是同一个引用
        // 因为它们是独立的作业。如果事件对象是序列化的，状态会传递。
        // 但是，更好的做法是确保 $event->user 已经被填充。
        if ($event->success && $event->user) { // 检查前一个操作是否成功
            dump('Verification email sent to ' . $event->user->email);
        } else {
            \Log::warning("Skipping email for {$event->email} due to previous failure.");
        }
    }
}