CloudKit: Efficient way to get user's rank in leaderboard without fetching all records?

The following flow should work:

• Add a record field to LeaderboardScore to hold the curent user record ID.
• Every time you generate a LeaderboardScore record, put the current user record ID there. You can get the information by calling fetchUserRecordID.
• Use the current user record ID to fetch the LeaderboardScore record, and retrieve the rank of the current user from there.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

Thank you for the response! I think there may be a slight misunderstanding of my question.

I am already linking each LeaderboardScore record to a user via a reference field. My challenge is how to efficiently calculate and determine the user’s rank, since I am not storing a rank field in the records and instead compute it client-side.

Please see attached photo for visual reference.

Current Implementation

1. Fetch LeaderboardScore records sorted by score (descending):

let query = CKQuery(recordType: "LeaderboardScore", predicate: predicate)
query.sortDescriptors = [NSSortDescriptor(key: "score", ascending: false)]

1. Assign rank based on position in the sorted results:

entries = scores.enumerated().map { index, score in
    score.asLeaderboardEntry(
        rank: index + 1,  // Rank assigned client-side
        isCurrentUser: score.profile.id == currentProfileID
    )
}

This works well when the current user is within the fetched results (e.g., top 15–20). In that case, I can determine their rank directly from the local data.

However, if the user is ranked further down (e.g., #247), I would need to paginate through results until reaching their record to determine the rank. This does not seem efficient or scalable.

Core Question

Given this setup:

• What is the recommended way to determine a user's rank when they are not within the initially fetched results?
• Is there an efficient way to compute rank without paginating through all higher-scoring records?
• Alternatively, is storing and maintaining a rank field the expected approach in CloudKit for this use case?

Additional Concern

If rank were to be stored, I'm unsure how it could be maintained efficiently. When a user submits a new score, assigning a rank would require knowing the relative position of all other users and potentially updating their ranks as well, which seems expensive and difficult to keep consistent.

Do you think this use case is not well-suited for CloudKit and would require a custom backend? I chose CloudKit to avoid building backend infrastructure, but I’m open to reconsidering that approach if it’s the recommended solution for implementing leaderboards with such features.

Oh, I thought that the score was the rank. Now that I understand it is actually the order in the result set sorted by score. Thanks for your elaboration.

In that case, you can probably try CKQuerySubscription, which allows you to observe the changes on LeaderboardScore and implement the following flow:

1. Set up a CKQuerySubscription to get notified of any changes on LeaderboardScore. Use the desiredKeys property of CKSubscription.NotificationInfo to specify the fields to include in the notification’s payload, which will be score and userID here.

2. Do an initial fetch to retrieve all the users and their scores you currently have.

3. When getting a notification of the subscription, grab the score and userID from the payload and update your local cache.

The only thing I am not quite sure about CKQuerySubscription is if the system always delivers the notifications to all users (other than the user who made the change) successfully. I think only real-world testing can tell – If you get a chance to try, please share your observation.

Other than that, I don't see anything better than your current implementation, which queries records with scores higher than the current user's score and counts them, with desiredKeys being set to [].

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.