New sync rule functions: json_keys and substring

[rkistner]

The substring function roughly matches the SQLite substring function (notably different from the JavaScript equivalent). It is also similar to the Postgres substring function, but different when a negative start or length is specified.

The json_keys function has no direct equivalent in Postgres or SQLite. Postgres has a similar json_object_keys, but that returns each key as a separate row, while we return the keys as a JSON array.

Use cases:

substring:

-- Parameter query - filter by date value
-- substring(created_at, 1, 10) returns the date portion of the timestamp
select id as post_id from posts where substring(created_at, 1, 10) in request.jwt() -> 'sync_dates'

json_keys:

-- Data query - permissions_json: {[user_id]: 'read' | 'write' | 'admin'}
-- This is still limited - we can only operate on the keys, and not the values
select * from items where bucket.user_id in json_keys(permissions_json)

-- even better would be something like this, but that is significantly more complex to implement:
select * from items where (permissions_json ->> bucket.user_id) = 'read'
select * from items where 'read' in (permissions_json ->> bucket.user_id)

[changeset-bot]

🦋 Changeset detected

Latest commit: 0f90b02

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

This PR includes changesets to release 4 packages

Name	Type
@powersync/service-sync-rules	Minor
@powersync/service-core	Patch
@powersync/service-image	Patch
test-client	Patch

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[stevensJourney]

This is awesome. It will help a lot with defining sync rules.

[guillempuche]

Cooool!!!