Listening to Events

Overview

A way to listen to events in Symfony projects is via an event subscriber, which is a class that defines one or more methods that listen to one or various events. This guide explains how to create event subscriber in your Shopware extension.

Use an event subscriber when your plugin needs to react to an event that Shopware already dispatches, for example, after an entity was loaded or written. Subscribers are intended for observation and enrichment; they are not a replacement for decorating a service when you need to change the existing control flow. If you only need to listen to one event, an event listener can be simpler. See the plugin fundamentals for a feature-selection overview.

Prerequisites

In order to build your own subscriber for your plugin, of course, you first need a plugin as a base. To create your own plugin, you can refer to the Plugin Base Guide.

INFO

For Academy learning content on Shopware events, subscribers, and dependency injection, refer to our free course Events and DI from Shopware Backend Development Intermediate learning path.

Creating your own subscriber

Plugin base class

Registering a custom subscriber requires loading a services.php file with your plugin. This is done by either placing a file with name services.php into a directory called src/Resources/config/.

Basically, that's it already if you're familiar with Symfony subscribers. Don't worry, we got you covered here as well.

Creating your new subscriber class

To start creating a subscriber, we need to create a class first implementing EventSubscriberInterface. As mentioned above, such a subscriber for Shopware 6 looks exactly the same as in Symfony itself.

Therefore, this is what your subscriber could then look like:

// <plugin root>/src/Subscriber/MySubscriber.php
<?php declare(strict_types=1);

namespace Swag\BasicExample\Subscriber;

use Shopware\Core\Content\Product\ProductEvents;
use Shopware\Core\Framework\DataAbstractionLayer\Event\EntityLoadedEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class MySubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        // Return the events to listen to as array like this:  <event to listen to> => <method to execute>
        return [
            ProductEvents::PRODUCT_LOADED_EVENT => 'onProductsLoaded'
        ];
    }

    public function onProductsLoaded(EntityLoadedEvent $event)
    {
        // Do something
        // E.g. work with the loaded entities: $event->getEntities()
    }
}

In this example, the subscriber would be located in the <plugin root>/src/Subscriber directory.

The subscriber is now listening for the product.loaded event to trigger.

Some entities, like orders or products, are versioned. This means that some events are dispatched multiple times for different versions, but they belong to the same entity. Therefore, you can check the version of the context to make sure you're only reacting to the live version.

// <plugin root>/src/Subscriber/MySubscriber.php
<?php declare(strict_types=1);

namespace Swag\BasicExample\Subscriber;

use Shopware\Core\Content\Product\ProductEvents;
use Shopware\Core\Defaults;
use Shopware\Core\Framework\DataAbstractionLayer\Event\EntityWrittenEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class MySubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        return [
            ProductEvents::PRODUCT_WRITTEN_EVENT => 'onProductWritten'
        ];
    }

    public function onProductWritten(EntityWrittenEvent $event)
    {
        if ($event->getContext()->getVersionId() !== Defaults::LIVE_VERSION) {
            return;
        }
        // Do something
    }
}

Unfortunately, your subscriber is not even loaded yet - this will be done in the previously registered services.php file.

WARNING

Creating the subscriber class alone is not enough. It must be registered in the dependency injection container and tagged with kernel.event_subscriber. If the class is missing from services.php, Shopware will not call it and there may be no obvious error indicating that the event was not handled.

Registering your subscriber via services.php

Registering your subscriber to Shopware 6 is also as simple as it is in Symfony. You're simply registering your (subscriber) service by mentioning it in the services.php. The only difference to a normal service is that you need to add the kernel.event_subscriber tag to your subscriber for it to be recognized as such.

// <plugin root>/src/Resources/config/services.php
<?php declare(strict_types=1);

use Swag\BasicExample\Subscriber\MySubscriber;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return static function (ContainerConfigurator $configurator): void {
    $services = $configurator->services();

    $services->set(MySubscriber::class)
        ->tag('kernel.event_subscriber');
};

That's it, your subscriber service is now automatically loaded at runtime, and it should start listening to the mentioned events to be dispatched.