如何在Spring Data R2DBC中使用Fluent数据访问接口返回生成的ID

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-r2dbc</artifactId>
</dependency>

@Table("users")
public class User {
    @Id
    private Long id;

    private String name;

    // 省略其他字段和方法
}

public interface UserRepository extends ReactiveCrudRepository<User, Long> {
    Mono<User> save(User user);
}

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public Mono<Long> createUser(User user) {
        return userRepository.save(user)
                .flatMap(savedUser -> Mono.just(savedUser.getId()));
    }
}