Getting started with RxJava with sqlite

Question

I\'m in the process of learning RxJava and have went thru several articles and videos. I totally felt awesome of what RxJava can offer, so I think currently getting the sense of

Answer 1

I'm sure that there are going to be a bunch of other opinions, but so far, I've taken a couple of different approaches:

• If you want a relatively small amount of data (and you can guarantee that it will always have a known upper bound on size), then:

  • create a synchronous method that accesses the database, gets a cursor, iterates the cursor to create a data structure (e.g. a List) containing the data, and then returns it.
  • Create a Callable that invokes the method
  • Use rx.fromCallable to create an an Observable

• If you need an unbounded number of rows, do something similar to the above, but return the Cursor.

EDIT: sample code:

private Map<String, String> getDataFromDatabase() { 
   Map<String, String> result = new HashMap<>(); 
   // do whatever you need to (i.e. db query, cursor) to fill it in 
   return result; 
} 

private Callable<Map<String, String>> getData() { 
   return new Callable() { 
      public Map<String, String> call() { 
        return getDataFromDatabase(); 
    } 
}

// in utility class  RxUtil.java 
public static <T> Observable<T> makeObservable(final Callable<T> func) {
        return Observable.create(
                new Observable.OnSubscribe<T>() {
                    @Override
                    public void call(Subscriber<? super T> subscriber) {
                        try {
                            T observed = func.call();
                            if (observed != null) { // to make defaultIfEmpty work
                                subscriber.onNext(observed);
                            }
                            subscriber.onCompleted();
                        } catch (Exception ex) {
                            subscriber.onError(ex);
                        }
                    }
                });
    }


// and finally, 
public Observable<Map<String, String>> getDataObservable() {
   return RxUtil.makeObservable(getData());
}