Get random items from firebase min 3 max 5 - firebase

Question

I am trying to get random items from my firebase database and it almost works,
sometimes I only get one or two items when the minimum is 3 and max is 5.
Every item has an index and it's getting the items that startAt(startindex) and endAt(startIndex+randomNumber).
Is there any other way to do this other than using an index on each item in the database?
Here is how the code looks now:
randomNumber = getRandomInt(3,5);
listView = (ListView)view.findViewById(R.id.listView);
int startIndex = (int)(Math.random() * childs+1);
adapter = new FirebaseListAdapter<TraningData>(getActivity(),TraningData.class,R.layout.layout_traning_item,ref_1
.orderByChild("index")
.startAt(startIndex)
.endAt(startIndex+randomNumber)) {
#Override
protected void populateView(View view, final TraningData td, int i) {
//Populating over here!
}
};
listView.setAdapter(adapter);

Answer 1

Since Firebase never want to add this feature.
Here how I solved it by adding all to an array and then make a random selection.
ArrayList<TraningData> randomSelected = new ArrayList<>();
Random rand = new Random();
int numElements = getRandomInt(3,5);
for(int i = 0;i < numElements;i++){
int randomIndex = rand.nextInt(traningData.size());
randomSlected.add(traningData.get(randomIndex));
}
cAdapter = new CustomAdapter(getActivity(),randomSlected);
listView.setAdapter(cAdapter);