Android developer. Beer & coffee snob. Cultivator of beard. Berliner in training.

Loading a List of Objects from Firebase

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I’ve been working with Firebase lately in preparation for adding data synchronization to my Music Library app. Their docs did a great job of getting me set up. Using the sample app as a guide, I even got Google+ OAuth working without much trouble. From there, it didn’t take long to load data into a Firebase instance partitioned by Google account. All that was left was to query the data out of Firebase and I’d be able to see the sync magic in action.

As you probably guessed from the title of this post, fetching a collection of objects from Firebase was not quite as straightforward. The documentation on retrieving data covers the methods for executing asynchronous queries, but uses HashMap results instead of the objects I initially stored. Um…no thanks.

I eventually noticed an overload of the getValue() method of the DataSnapshot class that takes a GenericTypeIndicator<T> parameter. In the JavaDocs for that class, is the secret sauce:

GenericTypeIndicator<List<Beer>> typeIndicator = new GenericTypeIndicator<List<Beer>>() {};
List<Beer> beers = snapshot.getValue(typeIndicator);


Combining that with these awesome RxJava Firebase bindings, I can now load a list with something as simple as:

private Observable<List<Beer>> loadBeers() {
    Firebase firebase = new Firebase("https://some-instance.firebaseio.com/beers");
    GenericTypeIndicator<List<Beer>> typeIndicator = new GenericTypeIndicator<List<Beer>>() {};
    return RxFirebase.observe(firebase.orderByKey())
        .map(snapshot -> snapshot.getValue(typeIndicator));
}

Aside from this little hiccup, Firebase is hard to beat for easy persistence that automatically syncs across devices. I look forward to seeing what Google does with it.

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