根据文档symfony custom_normalizer，您可以为Note实体创建一个自定义规范化器（例如NoteNormalizer）。在supportsNormalization方法中，您必须通过提供Note实体类来明确规范器只会影响Note实体。因此，在normalize方法中，您将获得Note的ArrayCollection中的每一项。如果您想确定，你可以在这个normalize方法中对$data变量（dd（$data））进行转储，这样你就得到了ArrayCollection的第一个元素。这就是我试图理解它的方法。

namespace App\Serializer;

use App\Entity\Note;
use Symfony\Component\Serializer\Normalizer\ContextAwareNormalizerInterface;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

class NoteNormalizer implements ContextAwareNormalizerInterface
{
    private $normalizer;

    public function __construct(ObjectNormalizer $normalizer) // Like in documentation you can inject here some customer service or symfony service
    {
        $this->normalizer = $normalizer;
    }

    public function normalize($topic, $format = null, array $context = [])
    {
        $data = $this->normalizer->normalize($topic, $format, $context);

        $data['name'] = 'some name';
        $data['size'] = 12000;
        $data['nb_of_notes'] = 15;

        return $data;
    }

    public function supportsNormalization($data, $format = null, array $context = [])
    {
        return $data instanceof Note;
    }
}

或者，如果需要，可以使用以下命令自动生成：

php bin/console make:serializer:normalizer

并给予名称：注意规范化程序

只需创建一个“集合Normalizer“：

注意：对于vanilla symfony项目也是如此。

namespace App\Serializer;

use App\Entity\Note;
use Symfony\Component\Serializer\Normalizer\ContextAwareNormalizerInterface;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Normalizer\NormalizerAwareTrait;

class NoteCollectionNormalizer implements ContextAwareNormalizerInterface, NormalizerAwareInterface
{
    use NormalizerAwareTrait;

    public function supportsNormalization($data, $format = null, array $context = []): bool
    {
        if(!is_array($data) || (!current($data) instanceof Note)) {
            return false;
        }

        return true;
    }

    /**
     * @param Note[] $collection
     */
    public function normalize($collection, $format = null, array $context = [])
    {
        // ...
    }
}