omitIfEmpty example

class RelationshipNormalizer extends NormalizerBase {

  /** * {@inheritdoc} */
  public function normalize($object, $format = NULL, array $context = []): array|string|int|float|bool|\ArrayObject|NULL {
    assert($object instanceof Relationship);
    return CacheableNormalization::aggregate([
      'data' => $this->serializer->normalize($object->getData(), $format, $context),
      'links' => $this->serializer->normalize($object->getLinks(), $format, $context)->omitIfEmpty(),
      'meta' => CacheableNormalization::permanent($object->getMeta())->omitIfEmpty(),
    ]);
  }

  /** * {@inheritdoc} */
  public function hasCacheableSupportsMethod(): bool {
    @trigger_error(__METHOD__ . '() is deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. Use getSupportedTypes() instead. See https://www.drupal.org/node/3359695', E_USER_DEPRECATED);

    return TRUE;
  }

        ],
      ],
    ]);
    if ($data instanceof ErrorCollection) {
      $document['errors'] = $this->normalizeErrorDocument($object, $format, $context);
    }
    else {
      // Add data.       $document['data'] = $this->serializer->normalize($data, $format, $context);
      // Add includes.       $document['included'] = $this->serializer->normalize($object->getIncludes(), $format, $context)->omitIfEmpty();
      // Add omissions and metadata.       $normalized_omissions = $this->normalizeOmissionsLinks($object->getOmissions(), $format, $context);
      $meta = !$normalized_omissions instanceof CacheableOmission
        ? array_merge($object->getMeta(), ['omitted' => $normalized_omissions->getNormalization()])
        : $object->getMeta();
      $document['meta'] = (new CacheableNormalization($normalized_omissions, $meta))->omitIfEmpty();
    }
    // Add document links.     $document['links'] = $this->serializer->normalize($object->getLinks(), $format, $context)->omitIfEmpty();
    // Every JSON:API document contains absolute URLs.     return CacheableNormalization::aggregate($document)->withCacheableDependency((new CacheableMetadata())->addCacheContexts(['url.site']));
  }

// Keep only the requested fields (the cached normalization gradually grows     // to the complete set of fields).     $fields = $normalization_parts[ResourceObjectNormalizationCacher::RESOURCE_CACHE_SUBSET_FIELDS];
    $field_normalizations = array_intersect_key($fields, array_flip($field_names));

    $relationship_field_names = array_keys($resource_type->getRelatableResourceTypes());
    $attributes = array_diff_key($field_normalizations, array_flip($relationship_field_names));
    $relationships = array_intersect_key($field_normalizations, array_flip($relationship_field_names));
    $entity_normalization = array_filter(
      $normalization_parts[ResourceObjectNormalizationCacher::RESOURCE_CACHE_SUBSET_BASE] + [
        'attributes' => CacheableNormalization::aggregate($attributes)->omitIfEmpty(),
        'relationships' => CacheableNormalization::aggregate($relationships)->omitIfEmpty(),
      ]
    );
    return CacheableNormalization::aggregate($entity_normalization)->withCacheableDependency($object);
  }

  /** * Normalizes an entity using the given fieldset. * * @param string[] $field_names * The field names to normalize (the sparse fieldset, if any). * @param \Drupal\jsonapi\JsonApiResource\ResourceObject $object * The resource object to partially normalize. * @param string $format * The format in which the normalization will be encoded. * @param array $context * Context options for the normalizer. * * @return array * An array with two key-value pairs: * - 'base': array, the base normalization of the entity, that does not * depend on which sparse fieldset was requested. * - 'fields': CacheableNormalization for all requested fields. * * @see ::normalize() */