你可以使用PreWriteValidationEvent来抛出你的自定义异常或者抑制一个异常。但是无论哪种方式，你都必须首先检查非唯一的值。

class MyEntityValidationSubscriber implements EventSubscriberInterface
{
    private EntityRepository $myEntityRepository;

    public function __construct(EntityRepository $myEntityRepository) 
    {
        $this->myEntityRepository = $myEntityRepository
    }

    public static function getSubscribedEvents(): array
    {
        return [
            PreWriteValidationEvent::class => 'onPreWriteValidate',
        ];
    }

    public function onPreWriteValidate(PreWriteValidationEvent $event): void
    {
        foreach ($event->getCommands() as $command) {
            if ($command instanceof DeleteCommand || $command->getEntityName() !== 'my_entity') {
                continue;
            }

            $payload = $command->getPayload();

            if (!\array_key_exists('name', $payload)) {
                continue;
            }

            $criteria = new Criteria();
            $criteria->addFilter(new EqualsFilter('name', $payload['name']));
            $existingEntity = $this->myEntityRepository->searchIds($criteria, $event->getContext())->firstId();

            if ($existingEntity === null) {
                continue;
            }

            throw new MyEntityDuplicateNameException();
        }
    }
}

class MyEntityDuplicateNameException extends ShopwareHttpException
{
    public function __construct()
    {
        parent::__construct('Field name of my_entity must be unique.');
    }

    public function getErrorCode(): string
    {
        return 'MY_PLUGIN__MY_ENTITY_DUPLICATE_NAME';
    }

    public function getStatusCode(): int
    {
        return Response::HTTP_BAD_REQUEST;
    }
}