How to implement preference based notifications in laravel?

A few days back, I was asked to implement a pretty awesome notification system on one of my client's laravel application, we are calling it, Granular Preference for Notifications.

So the user story goes,

A user can select if they wish to receive a notification via email, broadcast, both or neither. We have a bunch of notifications like newletter, maintenance, invitations, messages etc. Some of these are important to some users, essential for others and outright annoying to some. So, this is a pretty useful and much needed feature.

How I approached this problem?

There is actually an existing laravel package which does something similar and looks promising. I looked at the package and was going use it but instead wanted to have something custom-made for our specific use case.

I figured what we need at most is some way to edit the via() method to return the appropriate channels based on what user has set in their profile.

The documentation shows something like this as well,

/**
 * Get the notification's delivery channels.
 *
 * @param  mixed  $notifiable
 * @return array
 */
public function via($notifiable)
{
    return $notifiable->prefers_sms ? ['nexmo'] : ['mail', 'database'];
}

How I solved this?

I created a new abstract class classed PreferenceBasedNotification.

<?php

namespace App\Notifications;

abstract class PreferenceBasedNotification extends Notification{
    final public function via($notifiable){}
    abstract public function toMail($notifiable);
    abstract public function toBroadcast($notifiable);
}

Every notification where a user can set a preference will inherit this abstract class and will have to implement toMail() and toBroadcast() and can't implement via() to fulfill the contract.

Why toMail() and toBroadcast() are abstract? It is to make sure that if a user is opting for both mail and broadcast then the notification has to provide it. For via() being final, I decided that individual notifications can not edit the logic to check user's channel preference.

Database Setup

I used two tables to achieve this, one keeps tracks of all the notifications where user can set a preference.

• preference_based_notifications

| event_text  | description | notification_class     |
|-------------|-------------|------------------------|
| New Message | ...         | NewMessageNotification |
| New Event   | ...         | NewEventNotification   |

• user_notification_preferences

| notification_id | user_id | receive_email | receive_notification |
|-----------------|---------|---------------|----------------------|
| 1               | 1       | true          | false                |
| 2               | 1       | true          | true                 |

Implementing the via() method

Now the only thing left to do is to implement via(). This method has to check for user preference and based on that return appropriate channel.

final public function via($notifiable)
{
    $viaChannels = [];
    $preference = $this->getPreference($notifiable->user_id);

    if ($preference->receive_email) {
        $viaChannels[] = 'mail';
    }
    if ($preference->receive_notification) {
        $viaChannels[] = 'broadcast';
    }

    return $viaChannels;
}

We can implement a method to check user's preference like this,

private function getPreference($userID)
{
    // get_class returns the class name with namespace
    // we need to get extract class name

    $currentClass = Arr::last(explode('\\', get_class($this)));

    $event = DB::table('notification_events')
        ->where('notification_class', $currentClass)->first();

    if (!$event) {
        return null;
    }

    return DB::table('user_notification_preferences')
        ->where('user_id', $userID)
        ->where('notification_event_id', $event->id)
        ->first();
}

And that's it. We can now look into the user_notification_preferences table and send notifications based on the user's choice.

You can checkout the gist here.