Hey All,
I have the following models:
class Company:
> name = models.CharField(max_length=200)
>
> class Event:
> title = models.CharField(max_length=200)
> company = models.ForeignKey(Company)
>
> class EventRegistration:
> attended = models.BooleanField(default=False)
> event = models.ForeignKey(Event)
Each Company can have several Events attached to it, and when people
register for an Event, an EventRegistration is created. If they actually
attend the Event, then that EventRegistration for that particular user is
set to "attended=True".
I'm currently generating reports, and what I need is essentially a way to
have the Company see all of their Events, and sort by the number of
attendees (EventRegistrations with "attended=True"). I have this SQL that
accomplishes what I need:
SELECT e.title FROM example_event e LEFT JOIN (SELECT event_id, COUNT(*)
> attendees FROM example_eventregistration WHERE attended=1 GROUP BY
> event_id) r ON (e.id=r.event_id) ORDER BY r.attendees DESC;
That gives me exactly what I want, which is a sorted list of Events. Well,
I really need more than just "e.title"; I actually need the whole object,
but this gives an idea of what I'm looking for. Is there any way to do this
in the Django ORM? I would need something like:
events.annotate(attendees=Count('eventregistration__attended=True')).order_by('attendees')
... I'm well aware that won't work, because you can't have conditions
within the string argument of Count(), but again, this is the idea of what
I want. Does anyone know the right way to do this? The "events" variable
needs to always have ALL of the Events from the Company, regardless of
whether anyone has attended that Event or not. The only difference is how
those Events are sorted (so events.filter(eventregistration__attended=True)will
not give me what I want, because that returns only a subset of Events).
Thanks in advance!
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