使用API平台的序列化组件Symfony Serializer来返回深层级联数据。

代码示例：

1. 创建一个序列化器类，命名为CustomSerializer.php

namespace App\Serializer;

use ApiPlatform\Core\Bridge\Doctrine\Orm\Paginator;
use ApiPlatform\Core\Exception\InvalidArgumentException;
use ApiPlatform\Core\JsonLd\Serializer\ContextTrait;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;

/**
 * A custom serializer that can handle deep association data.
 */
class CustomSerializer extends Serializer
{
    use ContextTrait;

    public function __construct(
        iterable $normalizers = [],
        iterable $encoders = []
    ) {
        $normalizers = array_merge($normalizers, [
            // Doctrine paginator normalizer
            new class() implements DenormalizerInterface {
                public function denormalize($data, $class, $format = null, array $context = []) : Paginator
                {
                    return Paginator::createFromCollection($data['data'], $data['totalItems'], $context['filters']['page'], $context['filters']['itemsPerPage']);
                }

                public function supportsDenormalization($data, $type, $format = null)
                {
                    return $type === Paginator::class && $format === 'jsonapi';
                }
            },
            // Object normalizer
            new ObjectNormalizer(null, null, null, null, null, null, $this->extractAttributesToSerialize([])),
        ]);

        parent::__construct($normalizers, $encoders);
    }

    /**
     * @param string $data
     * @param string $type
     * @param string $format
     * @param array $context
     * @return object
     * @throws InvalidArgumentException
     */
    public function deserialize($data, $type, $format = null, array $context = [])
    {
        if (strpos($format ?? '', 'json') !== false) {
            $data = $this->decode($data, $format);
        }

        return parent::deserialize($data, $type, $format, $this->createContext($format, $context));
    }

    /**
     * @param mixed $data
     * @param string $format
     * @param array $context
     * @return string
     * @throws InvalidArgumentException
     */
    public function serialize($data, $format = null, array $context = [])
    {
        $context += ['json_encode_options' => JsonResponse::DEFAULT_ENCODING_OPTIONS];
        $context = $this->createContext($format, $context);
        $context['ignored_attributes'] = $this->extractAttributesToSerialize($