The logic here is that if the ratings in the database are empty, then I want to get them from the API. I have the following code:
Observable.from(settingsRatingRepository.getRatingsFromDB())
.toList()
.switchIfEmpty(settingsRatingRepository.getSettingsRatingModulesFromAPI())
.compose(schedulerProvider.getSchedulers())
.subscribe(ratingsList -> {
view.loadRatingLevels(ratingsList, hideLocks);
}, this::handleError);
The getRatingsFromDB() call returns List<SettingRating>, but the API call returns Observable<List<SettingRating>>.
However, when I unit test this, when I pass an empty list from the database call, it does not execute the API call. Can someone pls help me in this matter. This is my unit test code:
when(mockSettingsRatingsRepository.getRatingsFromDB()).thenReturn(Collections.emptyList());
List<SettingsRating> settingsRatings = MockContentHelper.letRepositoryReturnSettingsRatingsFromApi(mockSettingsRatingsRepository);
settingsParentalPresenter.onViewLoad(false);
verify(mockView).loadRatingLevels(settingsRatings, false);
As #Kiskae mentioned, it's the fact that I am confusing an empty list with an empty Observable. Therefore, I have used the following which is what I want:
public void onViewLoad(boolean hideLocks) {
Observable.just(settingsRatingRepository.getRatingsFromDB())
.flatMap(settingsRatings -> {
if (settingsRatings.isEmpty()) {
return settingsRatingRepository.getSettingsRatingModules();
} else {
return Observable.just(settingsRatings);
}
})
.compose(schedulerProvider.getSchedulers())
.subscribe(ratingsList -> {
view.loadRatingLevels(ratingsList, hideLocks);
}, this::handleError);
}
Observable#toList() returns a single element. If the observable from which it gets its elements is empty, it will emit an empty list. So by definition the observable will never be empty after calling toList().
switchIfEmpty will only be called when your observer completes without emitting any items.
Since you are doing toList it will emit list object. Thats why your switchIfEmpty is never getting called.
If you want to get data from cache and fallback to your api if cache is empty, use concat along with first or takeFirst operator.
For example:
Observable.concat(getDataFromCache(), getDataFromApi())
.first(dataList -> !dataList.isEmpty());
Building on answer by #kiskae, your use of a toList() emits the elements aggregated as a single List.
There is an alternative to the use of Observable.just() + a flatMap here.
Observable.from will iterate over the list returned by your service and emit each individual items, so an Observable<Rating>. If said list is empty, it naturally produces an empty Observable. Your API call also produces an Observable<Rating>, and in both cases you want to reaggregate that back into a List<Rating> for further processing.
So just move the toList() from your original code down one line, after the switchIfEmpty calling the API:
Observable.from(settingsRatingRepository.getRatingsFromDB())
.switchIfEmpty(settingsRatingRepository.getSettingsRatingModulesFromAPI())
.toList()
.compose(schedulerProvider.getSchedulers())
.subscribe(ratingsList -> {
view.loadRatingLevels(ratingsList, hideLocks);
}, this::handleError);
Granted, that solution may produce a bit more garbage (as the db's List is turned into an Observable just to be turned into a new List later on).
Related
Our project use a external library. It has a method return FluxMap (since FluxMap is not completely public so just call it Flux):
Flux<MappedType> aFluxMap = Library.createMappingToMappedType();
I have to emit some objects to aFluxMap to get them converted to MappedType (it has private constructor, few setter), then I can:
aFluxMap.doOnNext(converted -> doJob(converted))
I expect that there is a method on Flux/Mono like:
aFluxMap.emit(myObj);
But I could not find any method like that.
I have searched "how to emit to flux dynamically", then there is a solution:
FluxProcessor p = UnicastProcessor.create().serialize();
FluxSink sink = p.sink();
sink.next(mess);
But seem that it emit to newly created flux (p), not my aFluxMap. So I want to ask is there any way to emit message to a existed Flux (or how to connect a FluxSink to a existed Flux, so that whenever FluxSink .next(mess), then the existed Flux get the message). Thank you
Note: please don't pay much attention to the stupidity of the library. We must use it
==========================================
UPDATE:
As #lkatiforis suggestion:
FluxProcessor p = //see above
Flux<MappedType> aFluxMap = Library.createMappingToMappedType();
p.flatMap(raw -> aFluxMap).subscribe();
I got another issue. Library.createMappingToMappedType() return a subscribed Flux with its source is UnicastProcessor (also subscribed).
When I call p.flatMap(raw -> aFluxMap), then internally aFluxMap get subscribed again cause its source also get subscribed again, so that I got an exception telling that "UnicastProcessor can be subscribe once". Any suggestion?
You can create a new stream and then merge the two streams into one by using one of these methods: merge, concat, zip, and their variants.
Here is an example:
Flux<MappedType> yourFlux = //...
Flux<MappedType> aFluxMap = Library.createMappingToMappedType();
Flux.merge(aFluxMap, yourFlux);
The merge operator executes a merging of the MappedType objects from the two provided publisher sequences.
Let's say that I have a method addVoteToSong like:
public Mono<Map<Song, VoteKind>> addVoteToSong(Principal principal, String songId, VoteKind voteKind) {
return
userRepository.findUserByUsername(principal.getName())
.doOnSuccess(song -> songRepository.findSongById(songId))
.doOnSuccess(vote -> voteRepository.add(Vote.builder().song()))
.//(the rest of the code)
}
I want to pass a result from the line:
userRepository.findUserByUsername(principal.getName())
and
.doOnSuccess(song -> songRepository.findSongById(songId))
to the built object in the line:
.doOnSuccess(vote -> voteRepository.add(Vote.builder().song(here result from findSongById).user(here result from findUserByUsername))
Here comes the question, is it possible to reuse previous API call result in the next doOnSuccess method or I should split find API calls at the same time, giving up on Reactor's cascading operations? On the internet, I have found examples with single save method without basing on the indirect result of the reactive stream and that's why question occurred. I will be grateful for suggestions on how to reach a goal.
Martin,
First of all, be aware that .doOnXXX are just callbacks that will be executed on some archived conditions. You should avoid putting a business logic inside of them.
Coming back to the question, the first idea that comes to my mind is to benefit from zip operator. So you have to put 2 publishers .findUserByUsername and .findSongById and combine the result using BiFunction. So you can try the following:
public Mono<Map<Song, VoteKind>> addVoteToSong(Principal principal, String songId, VoteKind voteKind) {
return Mono
.zip(
userRepository.findUserByUsername(principal.getName()),
songRepository.findSongById(songId),
(user, song) -> voteRepository.add(Vote.builder().song(song).user(user).build())
)
.flatMap(Function.identity())
// your code is here
}
I have been trying for a long time to execute this code on Android, looking for answers here but not successfully. I'm a beginner developer, and please understand me.
I make multiple requests using Retrofit2 and RXJava
There is the answer, JSON (Array), it's class CurrencyData in Java
[
{
"r030":978,"txt":"euro","rate":11.11111,"cc":"EUR","exchangedate":"25.09.2018"
}
]
MyAPI interface
#GET("/BankService/v1/statdirectory/exchange")
Observable<List<CurrencyData>> getCurrencyCodeDate(#Query("valcode") String valCode, #Query("date") String date);
collect requests
List<Observable<List<CurrencyData>>> requests = new ArrayList<>();
requests.add(myApi.getCurrencyCodeDate("USD","20180928"));
requests.add(myApi.getCurrencyCodeDate("EUR","20180928"));
execute requests
Observable
.zip(requests, Arrays::asList)
.toList()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
I got
[[CurrencyData{txt='Dollar USA', rate='1.111'}], [CurrencyData{txt='EURO', rate='2.222'}]]
I'm interested in how to get a List<CurrencyData> with all the CurrencyData objects.
I tried to use map and flatMap - but it does not work.
I will be very grateful.
Thank you.
Problem:
Your getCurrencyCodeDate method returns Observable of List<CurrencyData>, And you are using it inside a Observable.zip() whith zipper func as Arrays::asList.
What is happening is, Your getCurrencyCodeDate emits a List of objects and Arrays::asList is wrapping all the emitted Lists in a List. Resulting in Observable.zip() emitting List<List<>>.
On top of that .toList() operator is applied, which will again wrap emitted List<List<>> inside another List resulting in List<List<List<>>> as return type.
What you could do is, use merge operator instead of zip and use collectInto instead of toList.
Observable
.merge(requests)
.collectInto(new ArrayList<CurrencyData>(), ArrayList::addAll)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
How can I return an object or list after using Blocking.get() method in Ratpack?
Blocking.get(()->
xRepository.findAvailable()).then(x->x.stream().findFirst().get());
Above line returns void - I want to be able to do something like below so that it returns the object in the then clause. I tried adding a return statement but doesn't work.
Object x = Blocking.get(()->
xRepository.findAvailable()).then(x->x.stream().findFirst().get());
You can use map to work with the value when it's available.
Blocking.get(() -> xRepository.findAvailable())
.map(x -> x.stream().findFirst().get())
.then(firstAvailable -> ctx.render("Here is the first available x " + firstAvailable))
Ratpack's Promise<T> does not provide blocking operation like Promise.get() that blocks current thread and returns a result. Instead you have to subscribe to the promise object. One of the methods you can use is Promise.then(Action<? super T> then) which allows you to specify and action that will be triggered when given value is available. In above example we use ctx.render() as an action triggered when value from blocking operation is ready, but you can do other things as well.
I'm trying to filter a list which might or might not be empty (or the item is not in the list). inboxData is filled by another observable:
private BehaviorSubject<InboxResponse> inboxData = BehaviorSubject.create();
public Observable<Item> getInboxItem(String id) {
return inboxData
.flatMap(response -> Observable.from(response.getData()))
.filter(item -> item.getId().equals(id))
.firstOrDefault(null);
}
In this case if response.getData() is empty firstOrDefault never runs. But why? It clearly says that it gives you back the default value if the preceeding observable emits nothing.
firstOrDefault emits the default if the stream completes without any items being passed through the observable. For your stream to complete the BehaviorSubject would need to signal completion. Since there is no indication that happens it would never realize it needs to send the default.
The solution is to move the filter and firstOrDefault to the inside of the flatMap so the end of the list provided by getData ends up completing the inner stream.
Note that if you're using RxJava2 as your tags suggest, null can never be an item in the stream, so passing it as default would cause an exception.
public Observable<Item> getInboxItem(String id) {
return inboxData
.flatMap(response -> Observable.from(response.getData()))
At this point, response.getData() returns null, right?
.filter(item -> item.getId().equals(id))
That means that item here is null. So item.getId() throws a NullPointerException. An error like that is immediately passed to the subscriber's onError handler. The firstOrDefault method will not even be called anymore, because the stream is immediately terminated.
.firstOrDefault(null);
}