feat: Add a new `beforeLiveQueryEvent` trigger

[codeKonami]

Pull Request

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• Link this pull request to an issue.

Issue

Closes: https://github.com/parse-community/parse-server/issues/9431

Approach

I added a beforeLiveQueryEvent trigger which allows the user to modify the updated object before it is passed to the LiveQuery server (via PubSub). It is a cloned version of the object so it won't modify the one passed to the afterSave trigger.

I've added an option which I'm not really convinced. You can set the context of the request to req.context.preventLiveQuery === true to prevent the publish to be made by the Parse Server and so limiting some network and CPU consumption depending on some business logic.

Tasks

• [x] Add tests
• [ ] Add changes to documentation (guides, repository pages, code comments)
• [ ] Add security check
• [ ] Add new Parse Error codes to Parse JS SDK

Summary by CodeRabbit

• New Features

  • Introduced support for registering "before live query event" triggers, allowing custom logic to run before live query events are published.
  • Added the ability to prevent specific live query events from being sent by setting a context flag in the trigger.

• Bug Fixes

  • Improved context handling for triggers to ensure consistent behavior during live query events.

• Tests

  • Added comprehensive tests to verify the behavior and effects of the new "before live query event" triggers.

[parse-github-assistant[bot]]

Thanks for opening this pull request!

[mtrezza]

@codeKonami please let us know when this is ready for review and change the PR state.

[codeKonami]

@codeKonami please let us know when this is ready for review and change the PR state.

The code is ready, I'd be interested to have your opinion on the approach before going further on documentation and probably more unit tests.

[mtrezza]

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📝 Walkthrough

"""

Walkthrough

The changes introduce a new Parse Server trigger called beforeLiveQueryEvent. This trigger allows developers to execute custom logic before a LiveQuery event is published. The implementation includes a new registration method in the Parse Cloud SDK, integration of the new trigger type into the trigger handling system, and updates to the LiveQuery publishing flow to support conditional event suppression based on the trigger's outcome. Comprehensive tests have been added to verify correct triggering, context handling, object mutation, and the ability to prevent LiveQuery events.

Changes

File(s)	Change Summary
spec/ParseLiveQuery.spec.js	Added new test cases for beforeLiveQueryEvent trigger, testing execution, context, mutation, and event prevention.
src/RestWrite.js	Refactored runAfterSaveTrigger to async; integrated beforeLiveQueryEvent trigger before LiveQuery notification.
src/cloud-code/Parse.Cloud.js	Added ParseCloud.beforeLiveQueryEvent method for registering the new trigger.
src/triggers.js	Added beforeEvent trigger type; updated context handling in trigger execution to support the new trigger.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant ParseServer
    participant CloudCode
    participant LiveQueryServer

    Client->>ParseServer: Save or update object
    ParseServer->>CloudCode: Run beforeLiveQueryEvent trigger (if defined)
    alt beforeLiveQueryEvent sets preventLiveQuery
        CloudCode-->>ParseServer: preventLiveQuery = true
        ParseServer-->>LiveQueryServer: (No notification sent)
    else beforeLiveQueryEvent allows event
        CloudCode-->>ParseServer: allow event
        ParseServer->>LiveQueryServer: Notify LiveQuery event
    end
    ParseServer->>CloudCode: Run afterSave trigger (if defined)
    ParseServer-->>Client: Respond to save/update

Assessment against linked issues

Objective	Addressed	Explanation
Implement a beforeLiveQueryEvent trigger to allow conditional suppression of LiveQuery event publishing (#9431)	✅
Provide a registration method for the new trigger in the Cloud Code SDK (#9431)	✅
Integrate the new trigger into the event publishing flow and context handling (#9431)	✅
Add tests verifying trigger execution, context mutation, and event suppression (#9431)	✅
"""

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[parseplatformorg]

:tada: Snyk checks have passed. No issues have been found so far.

:white_check_mark: security/snyk check is complete. No issues have been found. (View Details)

[mtrezza]

@codeKonami Apologies for the long wait time; when you have some time, please take a look at the review comments.