spring - 如果 webflux mono 的条件在 kotlin 中为真，则仅在 mongo db 中存储用户

Question

我有以下问题。只有当用户的电子邮件不存在时，我才想通过响应式(Reactive) Spring 数据存储库将用户保存到 mongo db 中。

@Component("userService")
class UserService(private val repository: UserRepository){

        fun checkIfEMailExists(email: String): Mono<Boolean> {
                return repository.findByEMail(email).hasElement()
        }

        fun create(user: User): Mono<User> {
               //not sure how to do this bit here
               this.checkIfEMailExists(user.email)
               .filter{ it -> it == true}
               .map{repository.save(user)}  
        }  

}

所以，基本上我不确定我如何处理 bool 的 Mono 只有当它的值为真时才做某事(否则抛出异常)

Answer 1

首先，您的 MongoDB 存储库应该是响应式存储库并返回 Mono<User>或 Flux<User>对于那种签名:

public interface UserRepository extends ReactiveMongoRepository<User, String> {

    Mono<User> findByEmail(String email);
}

然后，您可以将该 react 类型与其他运算符链接起来，如下所示:

@Service
public class UserService {

    private final UserRepository userRepository;

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

    public Mono<User> create(User user) {
        return this.userRepository.findByEmail(user.getEmail())
                .flatMap(existingUser -> Mono.error(new UserAlreadyPresentException(existingUser.getEmail())))
                .then(this.userRepository.save(user));
    }

    class UserAlreadyPresentException extends RuntimeException {

        public UserAlreadyPresentException(String email) {
            super("User already present with email " + email);
        }
    }
}