Question: I started using Project reactor and one place where I'm struggling little is how do I combine things coming from Mono with Flux. Here's my use case: 

```
public interface GroupRepository {
       Mono<GroupModel> getGroup(Long groupId);
}

public interface UserRepository {
       Flux<User> getUsers(Set<Long> userIds);   
}

Mono<GroupModel> groupMono = getGroup(groupId);
Flux<User> userFlux = getUsers(Set<Long> users);
//run above instrtuction in parallel and associate user to group.

```

Now what I want to achieve is: 

How can I combine response from UserFlux and associate those users with that group, with something like group.addUsers(userfromFlux).

Can someone help with how to combine results coming from userFlux and groupMono. I think I use something like Zip but then it does one to one mapping from source. In my case, I need to do 1 to N mapping. Here I have one group but multiple user that I need to add to that group. Is it a good idea to return `Mono<List<Users>` and then use zip operator with both mono and provide a combinator as mentioned here  

`public static <T1, T2, O> Flux<O> zip(Publisher<? extends T1> source1,
 Publisher<? extends T2> source2,
 final BiFunction<? super T1, ? super T2, ? extends O> combinator)`?

Answer: 
I think `Flux.combineLatest` static method could help you there: since your `Mono` only ever emits 1 element, that element will always be the one combined with each incoming value from the `Flux`.

```
Flux.combineLatest(arr -> new Combination((GroupModel) arr[0], (User) arr[1]),
                   groupMono, userFlux);

```
Adding an answer for other folks, I used, `Flux.zip(groupMono, userMono(holding list of users), this::biFunctionToPopulateGroupWithUsers)`. I used this approach rather than as suggested by @Simon, since underlying group that holds users is a `HashSet` and adding users in a reactive way will not be thread safe. But if you've a thread safe data structure I would use suggestion by @Simon.