Bucket Parameters Lookup Fix

[stevensJourney]

Overview

For reference see Discord thread.

The resolved sync buckets would be missing entries which matched data after updating (moving) relational linked columns.

Root Cause

The getParameterSets method was not returning the correct parameter sets after updating a todo_list's list_id column. The query fetched all bucket_parameters that:

• Match the provided lookups (related to the input list_ids),
• Have _id values smaller than the current checkpoint, and
• Match the group_id (sync rules set).

The issue arose during the $group stage, where results were grouped by the key field alone. Since the key was not unique for different lookup values, updates introducing REMOVE entries with empty bucket_parameters could override valid entries, leading to incorrect results.

Steps to Reproduce

See the screenshot of the bucket_parameters collection in MongoDB before and after executing an UPDATE todos set list_id = 2 where id = 12.

Initial State:

Todo id=12 belongs to list id=10 with its corresponding lookup and bucket_parameters.
Todo id=11 belongs to list id=2.

The bucket_parameters entries match the input lookups for:

• list_id=10 => todo_id=12 and
• list_id=2 => todo_id=11

Update:

Update Todo id=12 to belong to list id=2..

This creates a bucket_parameters entry which now associates list_id=2 => todo_id=12 and a REMOVE bucket_parameters entry which removes the association of list_id=10 (lookup) to todo_id=12. The REMOVE entry is created after the new association.

Issue:

When grouping results by key, the REMOVE entry (with empty bucket_parameters) overrides valid entries with the same key but a different lookup (e.g., for list 2).

Refer to the attached screenshot for a clear visual of the issue:

Before the update: the relevant lookups for each todo item are valid.

After the update: A REMOVE operation appears, the grouping in the getParameterSets query will return the bucket_parameters for the last entry which is the empty array from the remove entry.

Solution

The $group stage was updated to use a composite _id object:

{ key: '$key', lookup: '$lookup' }

This ensures that each unique combination of key and lookup is preserved in the grouped results, preventing REMOVE entries from overriding valid data.

Verification
Tested the fix by reproducing the issue as described above.

After applying the fix, the query correctly groups results by both key and lookup, preserving the valid bucket_parameters for each combination.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2298b5c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@powersync/service-core	Patch
@powersync/service-image	Patch
@powersync/service-module-mongodb	Patch
@powersync/service-module-mysql	Patch
@powersync/service-module-postgres	Patch
test-client	Patch

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