# Django Event ID Routing and URL Handling

## How event_id is used in URLs and Routing

- The system uses event-specific URLs for registration and attendance marking, such as:
  - `/attendance/register/<event_id>/`  → Register for a specific event
  - `/attendance/mark/<event_id>/`      → Mark attendance for a specific event

- These routes are defined in `attendance/urls.py`:

    path('register/<int:event_id>/', views.register_user, name='register_user'),
    path('mark/<int:event_id>/', views.mark_attendance_for_event, name='mark_attendance_for_event'),

- The `event_id` is passed as a parameter to the corresponding Django view function.

## How the logic works in Django views

- In `register_user(request, event_id=None)`, the event is fetched using:
    event = get_object_or_404(Event, id=event_id)
  - The view checks if the event is upcoming and handles registration for that event only.
  - The user is registered for the event using a ManyToManyField (`user.events.add(event)`).

- In `mark_attendance_for_event(request, event_id)`, the event is fetched similarly, and the page only allows marking attendance for that event if it is upcoming.

- In `ajax_mark_attendance(request, event_id=None)`, the event is fetched and the logic ensures:
  - Only users registered for the event (user.events contains the event) can mark attendance for that event.
  - If not registered, a message is returned: "You are not registered for this event."

## Summary
- The event_id in the URL ensures all registration and attendance actions are event-specific.
- The backend logic enforces that only registered users can mark attendance for the correct event.