UuidResolver.php

<?php

namespace Drupal\serialization\EntityResolver;

use Drupal\Core\Entity\EntityRepositoryInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

/**
 * Resolves entities from data that contains an entity UUID.
 */
class UuidResolver implements EntityResolverInterface {
    
    /**
     * The entity repository.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * Constructs a UuidResolver object.
     *
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository.
     */
    public function __construct(EntityRepositoryInterface $entity_repository) {
        $this->entityRepository = $entity_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public function resolve(NormalizerInterface $normalizer, $data, $entity_type) {
        // The normalizer is what knows the specification of the data being
        // deserialized. If it can return a UUID from that data, and if there's an
        // entity with that UUID, then return its ID.
        if ($normalizer instanceof UuidReferenceInterface && ($uuid = $normalizer->getUuid($data))) {
            if ($entity = $this->entityRepository
                ->loadEntityByUuid($entity_type, $uuid)) {
                return $entity->id();
            }
        }
        return NULL;
    }

}