java - 方法引用 : cannot convert reactor. core.publisher.Mono 到reactor.core.publisher.Mono

Question

我有两个Mono -s，如果一个不为空(用户已经存在)，我想返回/抛出异常，或者返回 Mono<User>基于另一值的值(将设置和 DTO 数据复制到用户对象)。我写道:

public Mono<User> registerUser(UserRegistrationDto userRegistrationDto) {
        Mono<Settings> settingsMono = settingsService.getSettings();
        Mono<User> dbUserMono = userRepository.findByEmail(userRegistrationDto.getEmail());
    return dbUserMono.map(dbUser -> Mono.error(new AlreadyRegisteredException())).or(
                settingsMono.map(
                    settings -> validateDtoAndCreateUser(userRegistrationDto, settings)
                ).flatMap(userRepository::save)
            );

userRepository 是一个 Spring Data ReactiveMongoRepository。 validateDtoAndCreateUser 的签名是:private User validateDtoAndCreateUser(UserRegistrationDto userRegistrationDto, SiteSettings siteSettings)

不幸的是userRepository::save我得到:

Bad return type in method reference: cannot convert reactor.core.publisher.Mono<S> to reactor.core.publisher.Mono<? extends R>

我做错了什么？我是否在某个地方使用了错误的运算符？

Answer 1

这样做:

return dbUserMono.flatMap(dbUser -> Mono.<User>error(new AlreadyRegisteredException()))
                 .switchIfEmpty(settingsMono.map(
                    settings -> validateDtoAndCreateUser(userRegistrationDto, settings)
                  ).flatMap(userRepository::save));