Room Flowable does not emit data on insertion

Question

I am having difficulty understanding how Flowable works in Room. I have Dao methods like this

@Insert(onConflict = OnConflictStrategy.REPLACE)
void upsert(List<Site> sites);

@Query("SELECT * FROM site ORDER BY distance ASC")
Flowable<List<Site>> getSites();

I expect that whenever I call upsert subscriber to Flowable object returned by getSites() will always be called. Is my assumption true?

Here is how I am susbcribing to this flowable

private final Flowable<List<Site>> siteFlowable;
ApiService apiService;
FuelDatabase database;

@Override
public void getSites(boolean showOnlyKeySites) {
    // add sites from cache first, then fetch network -> update cache -> update ui
    disposable = siteFlowable.flatMap(Flowable::fromIterable)
        .filter(site -> site.isValid())
        .buffer(100, TimeUnit.MILLISECONDS, 20)
        .takeUntil(sites -> sites.size() == 0)
        .observeOn(AndroidSchedulers.mainThread())
        .doOnNext(mapView::addPins)
        .subscribe(sites -> {
            Timber.d("Flowable emitted %d items", sites.size());
        }, Timber::e);

    apiService.getSites()
        .map(SiteListResponse::getData)
        .flatMap(Observable::fromIterable)
        .filter(Site::isValidSite)
        .toList().toObservable()
        .subscribe(sites -> {
            Timber.i("Success Fetching %d sites", sites.size());
            database.siteDao().clear();
            database.siteDao().upsert(sites);
        }, throwable -> Timber.e(throwable, "Error fetching sites"));
}

This flowable doesn't get called after upsert() is called. API is returning valid data and data is getting entered into database.

AFAIK Room queries are infinite thus `toList` won't work on them. See https://stackoverflow.com/a/47260768/61158 — akarnokd, Dec 26 '17 at 10:00
i think after toObservable() you need to use flatMap and covert upsert into another flowable stream — Rahul, Dec 26 '17 at 10:08
like flatMap(sites-> Flowable.just(upsert(sites))).subscribe — Rahul, Dec 26 '17 at 10:16
Isn't this your code? It's quite obviously there between `filter()` and `toObservable()`. Use CTRL+F to locate it. — akarnokd, Dec 26 '17 at 10:16
@Rahul Flowable should just emit items whenever there is a change in database, I don't wan't to manually do it. — Abhishek Bansal, Dec 26 '17 at 10:30
@AbhishekBansal for emitting item you need to call flowable.onNext(T) //T is generic here. can you past full code — Rahul, Dec 26 '17 at 10:33
`getSites` talks to a Room database, right? The Flowable returned by it is infinite and thus `toList` will never complete. — akarnokd, Dec 26 '17 at 10:33

score -1 · Answer 1 · answered Dec 26 '17 at 10:35

-1

Try this:

apiService.getSites()
    .map(SiteListResponse::getData)
    .flatMap(result -> 
         Observable.fromIterable(result)
        .filter(Site::isValidSite)
        .toList()
        .toFlowable()
    )
    .subscribe(sites -> {
        Timber.i("Success Fetching %d sites", sites.size());
        database.siteDao().clear();
        database.siteDao().upsert(sites);
    }, throwable -> Timber.e(throwable, "Error fetching sites"));

answered Dec 26 '17 at 10:35

akarnokd

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How will this enable `siteFlowable` to emit items? – Abhishek Bansal Dec 26 '17 at 10:38
Also `.buffer(100, TimeUnit.MILLISECONDS, 20)` could result in an empty list which you then use to stop the entire flow with `takeUntil()`. – akarnokd Dec 26 '17 at 10:41
@akarnod yes that might be causing it to emit only once. Also added definition in question. – Abhishek Bansal Dec 26 '17 at 10:43
You may have missing data. I suggest you read [this](https://proandroiddev.com/briefly-about-rxjava-logging-20308b013e6d) and apply `doOnNext`s at various places to figure out where data disappears. – akarnokd Dec 26 '17 at 10:48
`buffer` and `takeUntill()` were causing this issue. I had applied them because I did not want my `onNext` to be called too often. Removed them for time-being. – Abhishek Bansal Dec 26 '17 at 11:13

Room Flowable does not emit data on insertion

1 Answers1