I am accessing database using Maybe and my goal is to call the network if Maybe will complete indicating that there is no data in database (I am using room). I have following functions:
@Override
public Observable<List<Item>> getResults() {
return getResultsFromDatabase().toObservable().switchIfEmpty(getResultsFromNetwork());
}
@Override
public Observable<List<Item>> getResultsFromNetwork() {
System.out.println("getting results from network");
return api.getData().doOnNext(new Consumer<List<Item>>() {
@Override
public void accept(List<Item> items) throws Exception {
itemDao.insert(items);
}
});
}
@Override
public Maybe<List<Item>> getResultsFromDatabase() {
System.out.println("getting coins from database");
return itemDao.getAllItems();
}
However, the switchIfEmpty works a little unexpectedly, as it is always called, even though there are objects in database.
return getResultsFromDatabase().toObservable().switchIfEmpty(getResultsFromNetwork());
Use Single
instead of Maybe
. Because when there are no rows in db, Maybe
will be completed directly without calling error. But Single
will result in onError
with EmptyResultSetException
when there are no rows. We can then use Rx's power to return the data from network call. Here's how:
First change your itemDao.getAllItems()
to return Single<List<Item>>
.
Then change getResultsFromDatabase()
to return Single
as well like:
@Override
public Single<List<Item>> getResultsFromDatabase() {
System.out.println("getting coins from database");
return itemDao.getAllItems();
}
Now you need to use onErrorResumeNext
in order to return the data from network call, so change the getResults()
to:
@Override
public Observable<List<Item>> getResults () {
return getResultsFromDatabase()
.toObservable()
.onErrorResumeNext(new ObservableSource<List<Item>>() {
@Override
public void subscribe(io.reactivex.Observer<? super List<Item>> observer) {
getResultsFromNetwork();
}
});
}
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