WebFlux：为什么我需要在CRUD中使用flatMap

Question

我在互联网上找到了例子，但这并没有给我充分的理解。使用WebFlux时的标准CRUD。

路由器：

@Configuration
public class PersonRouter {

    @Bean
    public RouterFunction<ServerResponse> route(PersonHandler handler) {
        return RouterFunctions
                .route(GET("/getAllPersons").and(accept(MediaType.APPLICATION_JSON)), handler::findAll)
                .andRoute(GET("/getPerson/{id}").and(accept(MediaType.APPLICATION_STREAM_JSON)), handler::findById)
                .andRoute(POST("/createPerson").and(accept(MediaType.APPLICATION_JSON)), handler::save)
                .andRoute(DELETE("/deletePerson/{id}").and(accept(MediaType.APPLICATION_JSON)), handler::delete);
    }

}

处理程序：

@Component
public class PersonHandler {

    private final PersonService personService;

    public PersonHandler(PersonService personService) {
        this.personService = personService;
    }

    public Mono<ServerResponse> findById(ServerRequest request) {
        String id = request.pathVariable("id");
        return ok()
                .contentType(MediaType.APPLICATION_JSON)
                .body(personService.getById(id), Person.class);
    }

    public Mono<ServerResponse> findAll(ServerRequest request) {
        return ok()
                .contentType(MediaType.APPLICATION_JSON)
                .body(personService.getAll(), Person.class);
    }

    public Mono<ServerResponse> save(ServerRequest request) {
        final Mono<Person> person = request.bodyToMono(Person.class);
        return ok()
                .contentType(MediaType.APPLICATION_JSON)
                .body(fromPublisher(person.flatMap(personService::save), Person.class));
    }

    public Mono<ServerResponse> delete(ServerRequest request) {
        String id = request.pathVariable("id");
        return ok()
                .contentType(MediaType.APPLICATION_JSON)
                .body(personService.delete(id), Void.class);
    }

}

@Repository
public interface PersonRepository extends ReactiveMongoRepository<Person, String> {
}

@Service
@Transactional
@AllArgsConstructor
public class PersonService {

    private final PersonRepository personRepository;

    public Flux<Person> getAll() {
        return personRepository.findAll().switchIfEmpty(Flux.empty());
    }

    public Mono<Person> getById(final String id) {
        return personRepository.findById(id);
    }

    public Mono update(final String id, final Person person) {
        return personRepository.save(person);
    }

    public Mono save(final Person person) {
        return personRepository.save(person);
    }

    public Mono delete(final String id) {
        final Mono<Person> dbPerson = getById(id);
        if (Objects.isNull(dbPerson)) {
            return Mono.empty();
        }
        return getById(id).switchIfEmpty(Mono.empty()).filter(Objects::nonNull).flatMap(personToBeDeleted -> personRepository
                .delete(personToBeDeleted).then(Mono.just(personToBeDeleted)));
    }
}

public Mono<ServerResponse> save(ServerRequest request) {
        final Mono<Person> person = request.bodyToMono(Person.class);
        return ok()
                .contentType(MediaType.APPLICATION_JSON)
                .body(fromPublisher(person.flatMap(personService::save), Person.class));
    }

final Mono<Person> person = request.bodyToMono(Person.class);

personService::save

我是对的还是这个说法错了？

Answer 1

为什么你需要平面地图。

这些是我的想法，答案不同取决于你是在单声道还是通量上工作。

1.

public Mono<ServerResponse> influCRUD(ServerRequest req) {
    return req.bodyToMono(S.class) // the pipline begins with S class.
       .map(s -> {s.setF1(f1); s.setF2(f2); return s;}) // the pipeline has the same intput and output, i.e. object s, you use map.
       .flatMap(s -> webClient // the pipeline has S input, and T output, you use flatMap
            .post()
            .uri(uri)
            .body(BodyInserters.fromObject(s))
            .retrive()
            .bodyToMono(T.class) 
        ).flatMap(t -> ServerResponse // now the pipeline changes again, you use flatMap.
           .ok()
           .contentType()
           .body(BodyInserters.fromObject(t))
        );
}

和

mono flatMap（函数<？super T,？扩展mono<？扩展r>>转换器）

函数只执行a->b，当b是另一个producer/subsciber的输出时（当您使用反应式编程时，这种情况很可能发生），如前一个示例中的WebClient部分，它是Mono或flux形式。通过使用flatMap，它为您返回mono ，其中map返回mono ，正如它们在函数声明中所述。