Spring webflux - how to return a DTO in a mono by looking up two concurrent calls that return a Mono and a Flux?

Question

Somewhat new to reactive programming and can't find any good examples of this. How would I combine results from a Mono and a Flux (concurrent fetches) to return a Mono of a DTO?

I know the code below won't compile but generally speaking I want to do something like the below.

Thanks in advance.

public Mono<UserDto> getByName(String name) {
    Mono<User> user = userRepo.findByName(name);
    Flux<PhoneNumber> numbers = phoneNumbersRepo.findByName(name);

    return Mono.zip(user, number) ... 
               UserDto dto = new UserDto();
               dto.setFirstName(user.getFirstName());
               dto.setPhoneNumbers(number);

}

Answer 1

You would need to transform Flux<PhoneNumber> into Mono<List<PhoneNumber>> and then combine using Mono.zip

public Mono<UserDto> getByName(String name) {
    Mono<User> user = userRepo.findByName(name);
    Flux<PhoneNumber> numbers = phoneNumbersRepo.findByName(name);

    return Mono.zip(user, numbers.collectList())
            .map(res -> {
                UserDto dto = new UserDto();
                dto.setFirstName(res.getT1().getFirstName());
                dto.setPhoneNumbers(res.getT2());
                return dto;
            });
}