v2.1 The Event System

The Event System

API Platform Core implements the Action-Domain-Responder pattern. This implementation is covered in depth in the Creating custom operations and controllers chapter.

Basically, API Platform Core execute an action class that will return an entity or a collection of entities. Then a series of event listeners are executed which validate the data, persist it in database, serialize it (typically in a JSON-LD document) and create an HTTP response that will be sent to the client.

To do so, API Platform Core leverages events triggered by the Symfony HTTP Kernel. You can also hook your own code to those events. They are handy and powerful extension points available at all points of the request lifecycle.

In the following example, we will send a mail each time a new book is created using the API:

// src/AppBundle/EventSubscriber/BookMailSubscriber.php

namespace AppBundle\EventSubscriber;

use ApiPlatform\Core\EventListener\EventPriorities;
use AppBundle\Entity\Book;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent;
use Symfony\Component\HttpKernel\KernelEvents;

final class BookMailSubscriber implements EventSubscriberInterface
    private $mailer;

    public function __construct(\Swift_Mailer $mailer)
        $this->mailer = $mailer;

    public static function getSubscribedEvents()
        return [
            KernelEvents::VIEW => ['sendMail', EventPriorities::POST_WRITE],

    public function sendMail(GetResponseForControllerResultEvent $event)
        $book = $event->getControllerResult();
        $method = $event->getRequest()->getMethod();

        if (!$book instanceof Book || Request::METHOD_POST !== $method) {

        $message = (new \Swift_Message('A new book has been added'))
            ->setFrom('[email protected]')
            ->setTo('[email protected]')
            ->setBody(sprintf('The book #%d has been added.', $book->getId()));


If you use the official API Platform distribution, creating the previous class is enough. The Symfony Dependency Injection component will automatically register this subscriber as a service and will inject its dependencies thanks to the autowiring feature.

Alternatively, the subscriber must be registered manually.

Doctrine events are also available (if you use it) if you want to hook at the object lifecycle events.

Built-in event listeners are:

NameEventPre & Post hooksPriorityDescription
AddFormatListenerkernel.requestNone7guess the best response format (content negotiation)
ReadListenerkernel.requestPRE_READ, POST_READ4retrieve data from the persistence system using the data providers
DeserializeListenerkernel.requestPRE_DESERIALIZE, POST_DESERIALIZE2deserialize data into a PHP entity (GET, POST, DELETE); update the entity retrieved using the data provider (PUT)
ValidateListenerkernel.viewPRE_VALIDATE, POST_VALIDATE64validate data (POST, PUT)
WriteListenerkernel.viewPRE_WRITE, POST_WRITE32if using the Doctrine ORM, persist data (POST, PUT, DELETE)
SerializeListenerkernel.viewNone16serialize the PHP entity in string according to the request format
RespondListenerkernel.viewPRE_RESPOND, POST_RESPOND8transform serialized to a Symfony\Component\HttpFoundation\Response instance
AddLinkHeaderListenerkernel.responseNone0add a Link HTTP header pointing to the Hydra documentation
ValidationExceptionListenerkernel.exceptionNone0serialize validation exceptions in the Hydra format
ExceptionListenerkernel.exceptionNone-96serialize PHP exceptions in the Hydra format (including the stack trace in debug mode)

Those built-in listeners are always executed for routes managed by API Platform. Registering your own event listeners to add extra logic is convenient.

The ApiPlatform\Core\EventListener\EventPriorities class comes with a convenient set of class’s constants corresponding to commonly used priorities:


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