feat: [FC-7879] add signal handler to save assignment dates to edx-when models

[kyrylo-kh]

NOTE: Depends on openedx/edx-when#347

Description

This PR introduces a new signal-based mechanism to automatically sync assignment due dates with the ContentDate model in edx-when when a course is published.

Key Features

• Signal Handler:

  • Listens to the course_published signal.
  • Triggers a background task (update_assignment_dates_for_course) after publish.

• Celery Task:

  • Fetches assignments via get_course_assignments.
  • Calls update_or_create_assignments_due_dates() to persist due dates to the ContentDate model.
  • Includes logging, error handling, and staff user validation.

Tests

Includes comprehensive test coverage for:

• New and existing assignment date records.
• Missing or invalid data (e.g., no title/date).
• Empty assignment lists and failure scenarios (e.g., policy creation errors).
• Graceful handling when no staff user is available.

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[e0d]

How does this receiver interact with the existing one?

https://github.com/raccoongang/edx-platform/blob/b8d7a3ef8ae2f8b25038493104e5af572a7098c8/openedx/core/djangoapps/course_date_signals/handlers.py#L166

[kyrylo-kh]

Both are connected to SignalHandler.course_published. They run in registration order: extract_dates first (sync, updates block dates in edx_when), then update_assignment_dates (only schedules a Celery task with on_commit). They don’t call each other; the new one defers work so the task runs after the publish (and extract_dates) have committed.

[e0d]

Can you unroll the call stack here and say what the transaction approach is? Shouldn't it be atomic per task? If not, why not?

[kyrylo-kh]

tasks.py:36 -> edx_when.api.update_or_create_assignments_due_dates(), which wraps the whole loop in a single transaction.atomic() (edx_when/api.py ~L592). So the task’s DB work is already one atomic transaction; no extra atomic is needed in the task.

[kyrylo-kh]

Tests are failing because of openedx/edx-when#347