Filtering Subscriptions

There are times when you'll need to filter out specific events based on the arguments provided by the client. To handle this, you can return a true/false from the filter function to indicate whether the client should receive the subscription. For instance, using the following example:

subscription onPostUpdated($post_id: ID!) {
  postUpdated(post_id: $post_id) {
    id
    title
    content
  }
}

To ensure only clients who are subscribed to a certain post_id receive an update, we can create a filter:

namespace App\GraphQL\Subscriptions;

use Nuwave\Lighthouse\Subscriptions\Subscriber;
use Nuwave\Lighthouse\Schema\Types\GraphQLSubscription;

final class PostUpdatedSubscription extends GraphQLSubscription
{
    public function filter(Subscriber $subscriber, mixed $root): bool
    {
        // Clients arguments when subscribing
        $args = $subscriber->args;

        // Ensure that the Post ($root) id matches
        // the requested `post_id`
        return $root->id == $args['post_id'];
    }
}

Only To Others

When building an application that utilizes event broadcasting, you may occasionally need to broadcast an event to all subscribers of a channel except for the current user. You may accomplish this using the filter function, this following snippet is equivalent to the toOthers() method from Laravel's broadcast helper (opens new window).

namespace App\GraphQL\Subscriptions;

use Nuwave\Lighthouse\Subscriptions\Subscriber;
use Nuwave\Lighthouse\Schema\Types\GraphQLSubscription;

final class PostUpdatedSubscription extends GraphQLSubscription
{
    /**
     * Filter which subscribers should receive the subscription.
     */
    public function filter(Subscriber $subscriber, mixed $root): bool
    {
        // Filter out the sender
        return $subscriber->socket_id !== request()->header('X-Socket-ID');
    }
}

When you initialize a Laravel Echo instance, a socket ID is assigned to the connection. If you are using a global Axios (opens new window) instance to make HTTP requests from your JavaScript application, the socket ID will automatically be attached to every outgoing request in the X-Socket-ID header. Then, you can access that in your filter function.

If you are not using a global Axios instance, you will need to manually configure your JavaScript application to send the X-Socket-ID header with all outgoing requests. You may retrieve the socket ID using the Echo.socketId() method:

const socketId = Echo.socketId();