Android Nested requests example: multiple requests, combine results


Suppose we have an API which allows us to get object metadata in single request (getAllPets), and other request which have full data of single resource (getSinglePet). How we can query all of them in a single chain?

public class PetsFetcher {

static class PetRepository {
    List<Integer> ids;

static class Pet {
    int id;
    String name;
    int weight;
    int height;

interface PetApi {

    @GET("pets") Observable<PetRepository> getAllPets();

    @GET("pet/{id}") Observable<Pet> getSinglePet(@Path("id") int id);


PetApi petApi;

Disposable petsDisposable;

public void requestAllPets() {

            .doOnSubscribe(new Consumer<Disposable>() {
                @Override public void accept(Disposable disposable) throws Exception {
                    petsDisposable = disposable;
            .flatMap(new Function<PetRepository, ObservableSource<Integer>>() {
                public ObservableSource<Integer> apply(PetRepository petRepository) throws Exception {
                    List<Integer> petIds = petRepository.ids;
                    return Observable.fromIterable(petIds);
            .flatMap(new Function<Integer, ObservableSource<Pet>>() {
                @Override public ObservableSource<Pet> apply(Integer id) throws Exception {
                    return petApi.getSinglePet(id);
            .subscribe(new Consumer<List<Pet>>() {
                @Override public void accept(List<Pet> pets) throws Exception {
                    //use your pets here
            }, new Consumer<Throwable>() {
                @Override public void accept(Throwable throwable) throws Exception {
                    //show user something goes wrong


void cancelRequests(){
    if (petsDisposable!=null){
        petsDisposable = null;