Notifications not working with mysql db enabled

[AhtishamShahid]

Issue: Forum v2 MySQL Backend Cannot Find Newly Created Discussion Posts

Description

When creating a new post in the discussion forum with the MySQL backend enabled, the notification Celery task fails with a ForumV2RequestError. The thread is successfully created and visible in the Discussions MFE, but Forum v2 cannot retrieve it when processing notifications.

Prerequisites

This issue occurs when the following features are enabled:

• MySQL backend for forums
• Forum and notification Tutor plugins, OR
• forum_v2.enable_mysql_backend feature flag

Steps to Reproduce

1. Enable the MySQL backend for forums
2. Ensure forum and notification features are active
3. Create a new post in the discussion forum
4. Observe the error when the notification Celery task is triggered

Error Details

The notification worker raises a ForumV2RequestError indicating the thread does not exist, despite being visible in the Discussions MFE.

Error Message:

ForumV2RequestError('Thread does not exist with Id: 5')

Stack Trace:

lms-worker-1  | Traceback (most recent call last):
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/forum/backends/mysql/api.py", line 916, in validate_object
lms-worker-1  |     instance = modelss[model].objects.get(pk=int(obj_id))
lms-worker-1  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/django/db/models/manager.py", line 87, in manager_method
lms-worker-1  |     return getattr(self.get_queryset(), name)(*args, **kwargs)
lms-worker-1  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/django/db/models/query.py", line 635, in get
lms-worker-1  |     raise self.model.DoesNotExist(
lms-worker-1  | forum.backends.mysql.models.CommentThread.DoesNotExist: CommentThread matching query does not exist.
lms-worker-1  | 
lms-worker-1  | The above exception was the direct cause of the following exception:
lms-worker-1  | 
lms-worker-1  | Traceback (most recent call last):
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/forum/api/threads.py", line 140, in get_thread
lms-worker-1  |     thread = backend.validate_object("CommentThread", thread_id)
lms-worker-1  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/forum/backends/mysql/api.py", line 918, in validate_object
lms-worker-1  |     raise ObjectDoesNotExist from exc
lms-worker-1  | django.core.exceptions.ObjectDoesNotExist
lms-worker-1  | 
lms-worker-1  | The above exception was the direct cause of the following exception:
lms-worker-1  | 
lms-worker-1  | Traceback (most recent call last):
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/celery/app/trace.py", line 453, in trace_task
lms-worker-1  |     R = retval = fun(*args, **kwargs)
lms-worker-1  |                  ^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/celery/app/trace.py", line 736, in __protected_call__
lms-worker-1  |     return self.run(*args, **kwargs)
lms-worker-1  |            ^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/edx_django_utils/monitoring/internal/code_owner/utils.py", line 195, in new_function
lms-worker-1  |     return wrapped_function(*args, **kwargs)
lms-worker-1  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/edx-platform/lms/djangoapps/discussion/rest_api/tasks.py", line 36, in send_thread_created_notification
lms-worker-1  |     thread = Thread(id=thread_id).retrieve()
lms-worker-1  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/edx-platform/openedx/core/djangoapps/django_comment_common/comment_client/models.py", line 68, in retrieve
lms-worker-1  |     self._retrieve(*args, **kwargs)
lms-worker-1  |   File "/openedx/edx-platform/openedx/core/djangoapps/django_comment_common/comment_client/thread.py", line 168, in _retrieve
lms-worker-1  |     response = forum_api.get_thread(
lms-worker-1  |                ^^^^^^^^^^^^^^^^^^^^^
lms-worker-1  |   File "/openedx/venv/lib/python3.11/site-packages/forum/api/threads.py", line 143, in get_thread
lms-worker-1  |     raise ForumV2RequestError(
lms-worker-1  | forum.utils.ForumV2RequestError: Thread does not exist with Id: 5

Root Cause

The issue originates in the notification task (send_thread_created_notification) when attempting to retrieve the thread. The MySQL backend's validate_object method fails to find the CommentThread record, triggering a cascade of exceptions:

1. CommentThread.DoesNotExist in the MySQL backend
2. ObjectDoesNotExist in the validation layer
3. ForumV2RequestError at the API level

Impact

• Notification system fails for new discussion posts
• Users do not receive notifications for forum activity
• Creates inconsistency between the Discussions MFE (where posts are visible) and the backend notification system