Firebase retrieve highest 100 score
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Firebase retrieve highest 100 score
This is a screen shot of my firebase:
I am trying to retrieve the highest 100 score in firebase database
I am using this code to add new node to firebase:
Map<String, String> post1 = new HashMap<String, String>();
post1.put("name",name);
post1.put("score",score);
myRef.push().setValue(post1);
And this is the code I am using to retrieve the highest 100 score which doesn't work (the code works but it is not retrieving the highest 100 score)
Query queryRef = myRef.orderByChild("score").limitToFirst(100);
queryRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
Score score=postSnapshot.getValue(Score.class);
Log.d("test"," values is " + score.getName() + " " + score.getScore());
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
1 Answer
1
Firebase queries are always in ascending order. So you'll need to get the last 100, instead of the first 100.
Query queryRef = myRef.orderByChild("score").limitToLast(100);
Then client-side you'll need to reverse the items.
Alternatively you can add a inverted property to your items invertedScore: -99. If you do that, you can order by that inverted score and won't have to reverse the array.
invertedScore: -99
This scenario has been covered frequently before. I highly recommend you study some of these:
I'm wondering if this will actually work because in the question the scores are strings and not numbers. Won't it sort something like this: "1", "12", "2", "3", "33", "333", "4"?
– André Kool
Sep 14 '16 at 14:29
Darn.... good catch André. Apparently I have a blind spot, because I swear I checked whether they were stored as number. The above will indeed only work if you store the scores as number (or as zero-padded strings).
– Frank van Puffelen
Sep 14 '16 at 15:00
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It's better to store scores as number instead of strings. Check out the comments on frank's answer for more info.
– André Kool
Sep 15 '16 at 11:37