API Platform - onPreSerialize with MediaObject URI Resolver in normalization group - symfony

Question

I have a MediaObject exposed as a subresource within a normalization context group "modules":
/**
* #ApiResource(
* attributes={"access_control"="is_granted('ROLE_ADMIN')"},
* collectionOperations={
* "get",
* "post",
* "allData"={
* "method"="GET",
* "path"="/appdata",
* "normalization_context"={"groups"={"modules"}},
* "access_control"="is_granted('IS_AUTHENTICATED_ANONYMOUSLY')"
* }
* }
* )
* #ORM\Entity(repositoryClass="App\Repository\LearningModuleRepository")
* #UniqueEntity("identifier")
*
*/
class LearningModule
/**
* #ORM\Entity(
* repositoryClass="App\Repository\MediaObjectRepository"
* )
* #ApiResource(
* iri="http://schema.org/MediaObject",
* normalizationContext={
* "groups"={"media_object_read"},
* },
* attributes={"access_control"="is_granted('ROLE_ADMIN')"},
* collectionOperations={
* "post"={
* "controller"=CreateMediaObject::class,
* "deserialize"=false,
* "validation_groups"={"Default", "media_object_create"},
* "swagger_context"={
* "consumes"={
* "multipart/form-data",
* },
* "parameters"={
* {
* "in"="formData",
* "name"="file",
* "type"="file",
* "description"="The file to upload",
* },
* },
* },
* },
* "get",
* },
* itemOperations={
* "get",
* "delete"
* },
* )
* #Vich\Uploadable
*/
class MediaObject
/**
* #var string|null
*
* #ApiProperty(iri="http://schema.org/contentUrl")
* #Groups({"media_object_read", "modules"})
*/
public $contentUrl;
/**
* #var string|null
* #Groups({"modules"})
* #ORM\Column(nullable=true)
*/
public $filePath;
When exposed through the normalization group I only get filePath but not contentUrl. Im assuming the propblem has to do with the the ContentUrlSubscriber as outlined in the official docs:
public static function getSubscribedEvents(): array
{
return [
KernelEvents::VIEW => ['onPreSerialize', EventPriorities::PRE_SERIALIZE],
];
}
public function onPreSerialize(GetResponseForControllerResultEvent $event): void
{
$controllerResult = $event->getControllerResult();
$request = $event->getRequest();
if ($controllerResult instanceof Response || !$request->attributes->getBoolean('_api_respond', true)) {
return;
}
if (!($attributes = RequestAttributesExtractor::extractAttributes($request)) || !\is_a($attributes['resource_class'], MediaObject::class, true)) {
return;
}
$mediaObjects = $controllerResult;
if (!is_iterable($mediaObjects)) {
$mediaObjects = [$mediaObjects];
}
foreach ($mediaObjects as $mediaObject) {
if (!$mediaObject instanceof MediaObject) {
continue;
}
$mediaObject->contentUrl = $this->storage->resolveUri($mediaObject, 'file');
}
}
Does anybody have a clue how to handle the preSerialization in this case?
Thank You

Answer 1

I have found a solution to this problem:
The callback on PRE_SERIALIZE is aborted, since a LearningModule Object (not a MediaObject) has triggered the serialization ($attributes['resource_class'] === LearningModule).
To overcome this limitation, a decorated normalizer should be used as follows:
<?php
namespace App\Serializer;
use App\Entity\MediaObject;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Serializer\SerializerAwareInterface;
use Symfony\Component\Serializer\SerializerInterface;
use Vich\UploaderBundle\Storage\StorageInterface;
final class MediaObjectContentUrlNormalizer implements NormalizerInterface, DenormalizerInterface, SerializerAwareInterface
{
private $decorated;
private $storage;
public function __construct(NormalizerInterface $decorated, StorageInterface $storage)
{
if (!$decorated instanceof DenormalizerInterface) {
throw new \InvalidArgumentException(sprintf('The decorated normalizer must implement the %s.', DenormalizerInterface::class));
}
$this->decorated = $decorated;
$this->storage = $storage;
}
public function supportsNormalization($data, $format = null)
{
return $this->decorated->supportsNormalization($data, $format);
}
public function normalize($object, $format = null, array $context = [])
{
$data = $this->decorated->normalize($object, $format, $context);
if ($object instanceof MediaObject) {
$data['contentUrl'] = $this->storage->resolveUri( $object, 'file');
}
return $data;
}
public function supportsDenormalization($data, $type, $format = null)
{
return $this->decorated->supportsDenormalization($data, $type, $format);
}
public function denormalize($data, $class, $format = null, array $context = [])
{
return $this->decorated->denormalize($data, $class, $format, $context);
}
public function setSerializer(SerializerInterface $serializer)
{
if($this->decorated instanceof SerializerAwareInterface) {
$this->decorated->setSerializer($serializer);
}
}
}
Implementation details can be found here:
https://api-platform.com/docs/core/serialization/#decorating-a-serializer-and-adding-extra-data