Laravel 5.4, 5.3 : customize or extend notifications - database model

IMHO, the current Database channel for saving notifications in Laravel is really bad design:

You can't use foreign key cascades on items for cleaning up notifications of a deleted item for example
Searching custom attributes in the data column (casted to Array) is not optimal

How would you go about extending the DatabaseNotification Model in vendor package?

I would like to add columns event_id, question_id, user_id (the user that created the notification) etc... to the default laravel notifications table

How do you override the send function to include more columns?

In:

vendor/laravel/framework/src/Illuminate/Notifications/Channels/DatabaseChannel.php

The code:

class DatabaseChannel
{
 /**
  * Send the given notification.
  *
  * @param  mixed  $notifiable
  * @param  \Illuminate\Notifications\Notification  $notification
  * @return \Illuminate\Database\Eloquent\Model
  */
 public function send($notifiable, Notification $notification)
 {
    return $notifiable->routeNotificationFor('database')->create([
        'id' => $notification->id,
        'type' => get_class($notification),

      \\I want to add these
        'user_id' => \Auth::user()->id,
        'event_id' => $notification->type =='event' ? $notification->id : null, 
        'question_id' => $notification->type =='question' ? $notification->id : null,
      \\End adding new columns

        'data' => $this->getData($notifiable, $notification),
        'read_at' => null,
    ]);
 }
}

BassMHL

To create a custom Notification Channel:

First, create a Class in App\Notifications for example:

<?php

namespace App\Notifications;

use Illuminate\Notifications\Notification;

class CustomDbChannel 
{

  public function send($notifiable, Notification $notification)
  {
    $data = $notification->toDatabase($notifiable);

    return $notifiable->routeNotificationFor('database')->create([
        'id' => $notification->id,

        //customize here
        'answer_id' => $data['answer_id'], //<-- comes from toDatabase() Method below
        'user_id'=> \Auth::user()->id,

        'type' => get_class($notification),
        'data' => $data,
        'read_at' => null,
    ]);
  }

}

Second, use this channel in the via method in the Notification class:

<?php

namespace App\Notifications;

use Illuminate\Notifications\Notification;

use App\Notifications\CustomDbChannel;

class NewAnswerPosted extends Notification
{
  private $answer;

  public function __construct($answer)
  {
    $this->answer = $answer;
  }

  public function via($notifiable)
  {
    return [CustomDbChannel::class]; //<-- important custom Channel defined here
  }

  public function toDatabase($notifiable)
  {
    return [
      'type' => 'some data',
      'title' => 'other data',
      'url' => 'other data',
      'answer_id' => $this->answer->id //<-- send the id here
    ];
  }
}

Create and use your own Notification model and Notifiable trait and then use your own Notifiable trait in your (User) models.

App\Notifiable.php:

namespace App;

use Illuminate\Notifications\Notifiable as BaseNotifiable;

trait Notifiable
{
    use BaseNotifiable;

    /**
     * Get the entity's notifications.
     */
    public function notifications()
    {
        return $this->morphMany(Notification::class, 'notifiable')
                            ->orderBy('created_at', 'desc');
    }
}

App\Notification.php:

namespace App;

use Illuminate\Notifications\DatabaseNotification;

class Notification extends DatabaseNotification
{
    // ...
}

App\User.php:

namespace App;

use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    // ...
}

Unlike "Bassem El Hachem", I wanted to keep the database keyword in the via() methods.

So in addition to a custom DatabaseChannel, I also wrote my own ChannelManager that returns my own DatabaseChannel in the createDatabaseDriver() method.

In my apps' ServiceProvider::register() method, I overwrote the singleton for the original ChannelManager class to return my custom manager.

An example for @cweiske response.

If you really need extends the Illuminate\Notifications\Channels\DatabaseChannel not creating a new Channel you can:

Extends the channel:

<?php

namespace App\Notifications;

use Illuminate\Notifications\Channels\DatabaseChannel as BaseDatabaseChannel;
use Illuminate\Notifications\Notification;

class MyDatabaseChannel extends BaseDatabaseChannel
{
    /**
     * Send the given notification.
     *
     * @param  mixed  $notifiable
     * @param  \Illuminate\Notifications\Notification  $notification
     * @return \Illuminate\Database\Eloquent\Model
     */
    public function send($notifiable, Notification $notification)
    {
        $adminNotificationId = null;
        if (method_exists($notification, 'getAdminNotificationId')) {
            $adminNotificationId = $notification->getAdminNotificationId();
        }

        return $notifiable->routeNotificationFor('database')->create([
            'id' => $notification->id,
            'type' => get_class($notification),
            'data' => $this->getData($notifiable, $notification),

            // ** New custom field **
            'admin_notification_id' => $adminNotificationId,

            'read_at' => null,
        ]);
    }
}

And register the Illuminate\Notifications\Channels\DatabaseChannel on application container again:

app\Providers\AppServiceProvider.php

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

    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->bind(
            Illuminate\Notifications\Channels\DatabaseChannel::class,
            App\Notifications\MyDatabaseChannel::class
        );
    }
}

Now when the Illuminate\Notifications\ChannelManager try createDatabaseDriver will return your registered database driver.