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Single.concat report error and continue to the next

I'm trying to use RxJava with Android to asynchronously update my view. When user clicks the movie from the list in the RecyclerView, I want to present him first with the movie from the database, if present. Then I want to fetch the latest information and update the database as well as UI. I'm trying to use concat method and its variant but it does not work.
I have skipped other codes only to post the relevant RxJava methods that are fetching data as the rest is working fine.
When I disable network connection with the code below (hence remote returns error), the code below does not display data from the database at all. Only it reports the error. Which means the local is not resolving.
public Flowable<Movie> getMovie(final int id) {
return Single.concat(mLocal.getMovie(id), mRemote.getMovie(id).doOnSuccess(data -> {
mLocal.save(data);
})).onErrorResumeNext(error->{
return Flowable.error(error);
});
}
And in this code, it works fine, except now that I don't get the error message (and rightly so, since I have replaced it with new stream from the database)
public Flowable<Movie> getMovie(final int id) {
return Single.concat(mLocal.getMovie(id), mRemote.getMovie(id).doOnSuccess(data -> {
mLocal.save(data);
})).onErrorResumeNext(error->{
return mLocal.getMovie(id).toFlowable();
});
}
Now, how can I get database data first and then fire network call next to update data and get errors from the database or network call?
UPDATE
The latest method code
// calling getMovie on mLocal or mRemote returns Single
public Flowable<Movie> getMovie(final int id) {
return Single.concat(mLocal.getMovie(id), mRemote.getMovie(id).doOnSuccess(data -> {
mLocal.insertMovie(data);
})).onErrorResumeNext(error -> {
return Flowable.error(error);
});
}
Here is how I call them
public void loadMovie(int id)
{
Disposable d = mRepo.getMovie(id)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread(), true)
.doOnSubscribe(subscription -> {
subscription.request(Long.MAX_VALUE);
//post progress here
})
.subscribe(data -> {
//onNext
},
error -> {
//onError
},
() -> {
//onComplete
}
);
mDisposables.add(d);
}

With affirmation that my code works and guides on troubleshooting from #akarnokd I found the latest code (see OP) works flawlessly. The result of RxJava chain is posted to LiveData object which should update View. Unfortunately it only posts the latest data (which is an error) and skips the first (which is the data from the database).
I will deal with that but since the post deals with RxJava, I will consider this solved!

Rx concatWith() return only first Flowable result

I have posted all methods they are working separately , but I face issues with the first one, where I concatWith() two flowables
return userFavouriteStores()
.concatWith(userOtherStores())
.doOnNext(new Consumer<List<StoreModel>>() {
#Override
public void accept(#io.reactivex.annotations.NonNull List<StoreModel> storeModels) throws Exception {
Log.i("storeModels", "" + storeModels);
}
})
public Flowable<List<StoreModel>> userFavouriteStores() {
return userStores()
.map(UserStores::favoriteStores)
.flatMap(storeId -> storeDao.storesWithIds(storeId))
.map(stores -> { // TODO Konvert to Kotlin map {}
List<StoreModel> result = new ArrayList<>(stores.size());
for (se.ica.handla.repositories.local.Store store : stores) {
result.add(store.toStoreModel(StoreModel.Source.Favourite));
}
return result;
}); }
public Flowable<List<StoreModel>> userOtherStores() {
return userStores().map(UserStores::otherStores)
.flatMap(storeId -> storeDao.storesWithIds(storeId))
.map(stores -> {
List<StoreModel> result = new ArrayList<>(stores.size());
for (Store store : stores) {
result.add(store.toStoreModel(StoreModel.Source.Other));
}
return result;
});}
updated method :userStores() is used for favorite and other stores ,
private Flowable<UserStores> userStores() {
return apiIcaSeResource
.userStores()
.toFlowable(); }
#GET("user/stores")
Single<UserStores> userStores();

Following the comments follow up, and additional information, you don't have a problem specifically with the concat(), I'm assuming it is work, it's just not the tool for what you want to achieve here.
concat() will not concatenate two lists to a single list, but rathe will first emit all items by first Flowable and only then items emitted by second Flowable (hence you must have onComplete so concat will know when Flowable is end, what I asked in the begining).
in order to combine the lists together, I would suggest to zip both stores Obesrvables (favorites/ others), and then simply combine to list to have single output of combined list.
Besides that, as you pointed out, as both stores Observables comes from userStores(), you will invoke the network request twice, which definitely not necessary. you can solve it using publish(), that will share and multicast the network result to both Observables, resulting with single network request.
to sum it up, I would rather recommend to use Single here, not Flowable as you don't have backpressure consecrations. something like the following implementation:
Observable<List<StoreModel>> publish = userStores()
.toObservable()
.publish(userStores ->
Single.zip(
userFavouriteStores(userStores.singleOrError()),
userOtherStores(userStores.singleOrError()),
(favoriteStores, otherStores) -> {
favoriteStores.addAll(otherStores);
return favoriteStores;
}
)
.toObservable()
);

How to use RxJava to wait the end of two lists of Retrofit requests

Let me describe my situation:
I want to register new records via an API.
I want to update some records via an API.
I need to be notified when all of these requests have finished, to start another task.
Specifically I have two ArrayList:
ArrayList<Report> createdReports = myHelper.getOfflineCreatedReports();
ArrayList<Report> editedReports = myHelper.getOfflineEditedReports();
Each report can use methods to get Observable instances from my ApiService (Retrofit implementation).
Observable<NewReportResponse> createdReportsObs = Observable.from(createdReports) // .just() != .from()
.flatMap(new Func1<Report, Observable<NewReportResponse>>() {
#Override
public Observable<NewReportResponse> call(Report report) {
return report.postToServer();
}
});
Observable<NewReportResponse> editedReportsObs = Observable.from(editedReports)
.flatMap(new Func1<Report, Observable<NewReportResponse>>() {
#Override
public Observable<NewReportResponse> call(Report report) {
return report.updateInServer();
}
});
I am using the flatMap operator to get one Observable for each report.
But I am not sure how to wait until all of the requests have finished.
I was thinking in using the zip operator.
Observable.zip(createdReportsObs, editedReportsObs, new Func2<NewReportResponse, NewReportResponse, Boolean>() {
#Override
public Boolean call(NewReportResponse justOneResponse, NewReportResponse justOneResponse2) {
return false;
}
});
Unfortunately I saw some examples where zip is used to create pairs of Observables.
Please suggest me what operator I can use to achieve it. Or how to do it using rxJava with a different approach.
Thank you in advance.

Are you using RxJava 2? If so you can use the new completable api. This is assuming you don't need to know any of the server results, just need to wait for them to complete.
Completeable.merge(createdReportsObs.toCompleteable(),
editedReportsObs.toCompleteable())
.subscribe()

This is my way. May not best practice.
Observable.merge(createdReportsObs, editedReportsObs)
.toList()
.flatMap(Observable::from)
.xxx //Now they are completed, do what you want
.subscribe();

Filtering rx.Observable response into two different subscribers

I'm coding an Android App. I'm using Retrofit with RxJava in my network layer. Basically the issue that I have is that I have an endpoint called /feed. This endpoint returns a collection of articles that I show in a RecyclerView. Some of those articles are Ads articles, some are Events and others are Posts. I'm using a clean architecture, so I have an Interactor per each thing that I want to do. This is how my GetFeedInteractor looks like:
#Override
public void execute(final Callback callback, int offset, int pageSize) {
final String userSipId = mUserSipid.get();
mFeedRepository.getFeed(offset, pageSize)
.subscribe(new DefaultSubscriber<List<BaseFeedItem>>() {
#Override
public void onNext(List<BaseFeedItem> baseFeedItems) {
List<BaseFeedItem> cacheCollection = new ArrayList<BaseFeedItem>();
for (BaseFeedItem baseFeedItem : baseFeedItems) {
if (!(baseFeedItem instanceof AdFeedItem)) {
cacheCollection.add(baseFeedItem);
}
}
mFeedCache.saveFeeds(cacheCollection);
callback.onFeedsFetched(baseFeedItems);
}
});
}
As you can see the Callback that I use to show the items in the UI takes all the three types of Feeds and shows them. But I need to save only the Post articles and the Event articles in a Sqlite Cache. The thing is that I don't like doing that for instanceof inside the Subscriber. Is there some better Rx-way of doing this?
Update:
BTW I use the FeedCache#saveFeed method in several places, but only here is where I can get Ads Articles. So doing the Ad filtering inside the FeedCache#saveFeed is not a good choice.
Update2:
I think that the perfect solution for this would be if I could filter the collection using some of the Rx-methods, and have a Subscriber that handles the raw list, and another that handles the ad-filtered list. Something like that.

So, basically you want to 2 streams out of one stream. One will be the raw stream (for displaying UI), and the other will be a filtered stream (for saving in database). Unfortunately, you cannot have multiple onSubscribes, but we can use the concept of Subjects.
final PublishSubject<BaseFeedItem> subject = PublishSubject.create();
subject.subscribe(o -> {
// here will be emitted all items
// update the UI
});
mFeedRepository.getFeed(offset, pageSize)
.map(item -> {
subject.onNext(item);
return item;
})
.filter(item -> !(item instanceof AdFeedItem))
.subscribe(items -> {
// no `AddFeedItem`s here
// save into database
});

RxJava + retrofit, get a List and add extra info for each item

I'm playing around with RXJava, retrofit in Android. I'm trying to accomplish the following:
I need to poll periodically a call that give me a Observable> (From here I could did it)
Once I get this list I want to iterate in each Delivery and call another methods that will give me the ETA (so just more info) I want to attach this new info into the delivery and give back the full list with the extra information attached to each item.
I know how to do that without rxjava once I get the list, but I would like to practice.
This is my code so far:
pollDeliveries = Observable.interval(POLLING_INTERVAL, TimeUnit.SECONDS, Schedulers.from(AsyncTask.THREAD_POOL_EXECUTOR))
.map(tick -> RestClient.getInstance().getApiService().getDeliveries())
.doOnError(err -> Log.e("MPB", "Error retrieving messages" + err))
.retry()
.subscribe(deliveries -> {
MainApp.getEventBus().postSticky(deliveries);
});
This is giving me a list of deliveries. Now I would like to accomplish the second part.
Hope I been enough clear.
Thanks

Finally I found a nice way to do it.
private void startPolling() {
pollDeliveries = Observable.interval(POLLING_INTERVAL, TimeUnit.SECONDS, Schedulers.from(AsyncTask.THREAD_POOL_EXECUTOR))
.flatMap(tick -> getDeliveriesObs())
.doOnError(err -> Log.e("MPB", "Error retrieving messages" + err))
.retry()
.subscribe(this::parseDeliveries, Throwable::printStackTrace);
}
private Observable<List<Delivery>> getDeliveriesObs() {
return RestClient.getInstance().getApiService().getDeliveries()
.flatMap(Observable::from)
.flatMap(this::getETAForDelivery)
.toSortedList((d1, d2) -> {
if (d1.getEta() == null) {
return -1;
}
if (d2.getEta() == null) {
return 1;
}
return d1.getEta().getDuration().getValue() > d2.getEta().getDuration().getValue() ? 1 : -1;
});
}
Let's go step by step.
First we create an Observable that triggers every POLLING_INTERVAL time the method getDeliveriesObs() that will return the final list
We use retrofit to get an Observable of the call
We use flatMap to flattern the resut list and get in the next flatmap a Delivery item, one by one.
Then we get the estimated time of arrival set inside the Delivery object and return it
We sort the list to order by estimated time of arrival.
In case of error we print and retry so the interval does not stop
We subscribe finally to get the list sorted and with ETA inside, then we just return it or whatever you need to do with it.
It's working properly and it's quite nice, I'm starting to like rxjava :)

I haven't spent a lot of time with Java 8 lambdas, but here's an example of mapping each object to a different object, then getting a List<...> out at the other end in plain ol' Java 7:
List<Delivery> deliveries = ...;
Observable.from(deliveries).flatMap(new Func1<Delivery, Observable<ETA>>() {
#Override
public Observable<ETA> call(Delivery delivery) {
// Convert delivery to ETA...
return someEta;
}
})
.toList().subscribe(new Action1<List<ETA>>() {
#Override
public void call(List<ETA> etas) {
}
});
Of course, it'd be nice to take the Retrofit response (presumably an Observable<List<Delivery>>?) and just observe each of those. For that we ideally use something like flatten(), which doesn't appear to be coming to RxJava anytime soon.
To do that, you can instead do something like this (much nicer with lambdas). You'd replace Observable.from(deliveries) in the above example with the following:
apiService.getDeliveries().flatMap(new Func1<List<Delivery>, Observable<Delivery>>() {
#Override
public Observable<Delivery> call(List<Delivery> deliveries) {
return Observable.from(deliveries);
}
}).flatMap(...)