How can I efficiently retrieve a user’s rank from Firestore without scanning the entire collection?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I'm developing a Flutter app that displays the current user's rank based on their rating, which is stored in Firestore. My Firestore structure is as follows:

- Users (Collection)
-- UserId (Document ID)
--- rating (Field)

Problem:
I need to retrieve the rank of a specific player without reading all documents, especially as the number of users grows.

What I've tried so far:

Query all documents using orderBy and then calculate the rank locally:

This approach is inefficient because it reads the entire collection, which is not scalable.

Query with orderBy and limit:

This method works for leaderboard pagination but fails when a lower ranked player wants to check their own rank, since it still involves reading many documents.

Desired Outcome:
I want a scalable approach that retrieves the rank of one user without querying the whole collection. Are there better strategies or design patterns to achieve this?

Any suggestions or best practices are greatly appreciated.

Comments 0

•

Answers 2

•

2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Below is one common approach:

Count Documents with Higher Ratings:
Instead of reading all users to compute a rank, count only the number of users whose rating is higher than the current user’s rating. For example, if you know your user’s rating is X, then your rank is (number of users with a rating > X) + 1.

Using Firestore Aggregation (Count) Queries:
With the recent aggregation queries, you can ask Firestore to count matching documents without retrieving them. For example, you can run a query like:

DART
final currentUserRating = ...; // your user's rating

final Query query = FirebaseFirestore.instance
    .collection("Users")
    .where("rating", isGreaterThan: currentUserRating);

// Assuming you have the latest Firestore SDK that supports count() aggregation:
final aggregateQuery = query.count();
final aggregateQuerySnapshot = await aggregateQuery.get();
final higherRatingCount = aggregateQuerySnapshot.count;
final rank = higherRatingCount + 1;

This approach reads only the count instead of the full data set.

Maintain a Separate Leaderboard Structure:
In cases where aggregation is not optimal or available (or if you expect a very high frequency of rank reads/updates), you might consider maintaining a separate leaderboard document that’s updated via Cloud Functions on write. In that pattern, whenever a user’s rating changes, you update their ranking (or adjust a sorted leaderboard stored in a dedicated collection). This is a classic “data fan-out” pattern and can help you quickly retrieve ranks without performing a live count over a potentially huge collection.

Best Practices and Tradeoffs:

Aggregation queries are simple to implement but may have limits on concurrent usage and pricing (depending on your read operations).
Maintaining a leaderboard structure involves extra complexity (increased write load and the need for a backend process) but avoids running queries over large collections at read time.

Choose the method that best fits your app’s scale and update frequency. This way, you efficiently retrieve a single user’s rank without having to load the entire user collection.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

No comments yet.

Answer by CosmicWatcher217 • 1 month ago

I'm not quite sure what you're trying to do, you said you've already managed to get a paginated list of users, so i'm assuming you just want to get the signed in users rank, to do that, you'd only need to query firestore for one document, or if your user is already in the list of users you already have, you could get their rank by finding them in the list

Method 1 - Get the users doc

DART
Future<ParsedUser> _getUserAsync() async {
    // Get the users doc
    var userDoc = await Firestore.instance.collection('users').doc(FirebaseAuth.instance.user!.uid).get()

    // print the rank (just for debugging)
    var rank = userDoc['rank'];
    debugPrint(rank)

    // Change ParsedUser to your user class
    // I'm assuming you already have a fromJson function, if not then it's best
    // if you create one
    ParsedUser user = ParsedUser.fromJson(userDoc)

    return user;
}

Method 2 - Find the user in the list you already have

DART
ParsedUser? _getCurrentUser() {
    List<ParsedUser> users = [...] 

    // This will get the user from the list of users if the user exists in the list
    ParsedUser? currentUser = users.firstWhereOrNull((x) => x.id == FirebaseAuth.instance.user!.uid)

    return currentUser;
}

You could also combine them and check the list of users, and if the user isn't in there, then get them from firestore (more cost efficient)

DART
Future<ParsedUser> getUser() async {
   var user = _getCurrentUser();
   if (user != null) return Future.value(user);
 
   return await _getUserAsync();
}

No comments yet.

Discussion

No comments yet.

How can I efficiently retrieve a user’s rank from Firestore without scanning the entire collection?

2 Answers

Discussion

Similar Posts

Efficiently Retrieve a Flutter User's Rank from Firestore Without Scanning the Entire Collection