How to query where child does not exists in Firebase?

Question

Let's say that we have simple data structure:

"games": {
     "{gameId}" {
          "title": "Chess",
          "playedBy" : {
               "{userId}" : true,
               "{userId}" : true
           }
     }
}

There are just games and every game has data about users who played in this game. Now I want to get all games where specified user (let's say his id is "1234567") didn't play. I have to query games where "playedBy" does not contain "1234567".

How can I achieve that with Firebase?

Every language where Firebase works will be appreciated.

As far as I know there is no support for "not equals" operator in Firebase for now. — Ekalips, May 03 '17 at 11:38
Please check with this http://stackoverflow.com/questions/37752402/firebase-database-not-equal-request-alternative-solution-for-ios — , May 03 '17 at 11:48
Firebase can only query for values that are present. See http://stackoverflow.com/questions/28582223/is-it-possible-query-data-that-are-not-equal-to-the-specified-condition — Frank van Puffelen, May 03 '17 at 14:01

score 1 · Answer 1 · answered May 03 '17 at 12:14

You can do it like this:

Iterate trough all the games
Check if each game contains the user id

If not , add the game to list of games

mGamesRef.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
         if(!dataSnapshot.child("playedBy").hasChild(userId)) {
             gamesList.add(dataSnapshot.getValue(Game.class));
         }
    }
    ...

Hope this works for you.

Such disappointing solution... – Nominalista May 03 '17 at 12:30 — Nominalista, May 03 '17 at 12:30

How to query where child does not exists in Firebase?

1 Answers1