feat(schedule): add attendees count column to workshop admin list

[estyxx]

Summary

• Adds an Attendees column to the ScheduleItem admin list view, visible when filtering by type=training (workshops)
• Displays registered attendees as N / capacity when a capacity is set, or just N when there is none
• Annotates the queryset with Count("attendees", distinct=True) to avoid N+1 queries — a single SQL COUNT per row rather than a separate query per row

Test plan

• Open /admin/schedule/scheduleitem/?type__exact=training and verify the new Attendees column appears
• Check that items with attendees_total_capacity set show N / capacity format
• Check that items without a capacity show just the count

[vercel]

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Project	Deployment	Actions	Updated (UTC)
pycon	Error		May 15, 2026 2:59pm

[claude]

Adds an attendees_count column to the ScheduleItemAdmin list view showing registered attendees (and capacity when set), and refactors spaces_left to reuse the same queryset annotation.

Testing

No tests added for the new functionality:

• attendees_count() — both the "no capacity" and "with capacity" display branches are uncovered
• spaces_left() — the change from obj.attendees.count() to obj.attendees_count_annotation is a behaviour-affecting refactor with no test coverage; a regression here would be invisible

Error Handling

spaces_left and attendees_count both read obj.attendees_count_annotation directly. If a ScheduleItem object is ever fetched outside of the custom get_queryset (e.g. in a test, a signal handler, or a future change_view override), this raises AttributeError. The old obj.attendees.count() was unconditionally safe. A getattr(obj, 'attendees_count_annotation', None) fallback (or a comment marking the dependency) would prevent a hard crash.

Architecture

attendees_count is unconditionally in list_display, so it appears for talks, keynotes, and all other item types — not just trainings. Those rows will show 0 or 0 / N, which is misleading. A get_list_display() override that adds the column only when request.GET.get('type') == 'training' would make the intent match the implementation.

Minor

@admin.display on attendees_count could set ordering="attendees_count_annotation" to make the column sortable, which is the main usability reason to annotate rather than calling .count().

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.52%. Comparing base (b26753e) to head (8d5826e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4642   +/-   ##
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  Coverage   92.52%   92.52%           
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  Files         359      359           
  Lines       10791    10791           
  Branches      821      821           
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  Hits         9984     9984           
  Misses        696      696           
  Partials      111      111           

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