Query firebase realtime database where child has property

Question

I'm trying to query my Firebase Realtime Database to find all games a user belongs to.

I have a list of games , each game has a property of players . Each child of players has a key of $uid , and within that {key: $uid, name: "joe"}

Is it possible to get all games this way? Or do I need to start keeping another index of players_games/$uid/$game ?

I've tried firebase.database().ref('games').orderByChild('players').equalTo(token.uid) , but this yields null

It looks like database.ref('games').orderByChild('players/${token.uid}') works, but then I'd need to give .read access to all of games , or do this server-side.

Answer 1

Your current data structure makes it easy to find all the users for a specific game. It does not however make it easy to find all the games for a specific user. To allow that, you'll want to add an addition data structure that inverts the information.

So that'd look something like this:

player_games: {
  "XDYNyN8il6TDsM4LuttwDzNuytj1": {
    "-M5vf...U5zK": true
  },
  "NxH14...mxY2": {
    "-M5vf...U5zK": true
  }
}

Also see:

• Firebase query if child of child contains a value
• Firebase Query Double Nested

---

I recommend you also study the Firebase documentation on structuring your database , specifically the section on avoiding nested data . By mixing entity types as you currently do, you'll likely run into problems with security, and scalability.

The most idiomatic way to model your many-to-many relationship in the Firebase database is with four top-level lists:

players: {
  $playerId: { ... }
}
games: {
  $gameId: { ... }
}
player_games: {
  $playerId: {
    $gameId: true
  }
}
game_players: {
  $gameId: {
    $playerId: true
  }
}

Also see:

• Many to Many relationship in Firebase