Hello there,
You should be able to achieve what you're after by using annotations[0].
In your case you'll want to declare your Event and Reservation relationship
explicitly by using
a ForeignKey
class Event(models.Model):
...
seating = models.PositiveIntegerField(default=0)
class Reservation(models.Model):
...
event = models.ForeignKey(Event, related_name='reservations')
seats = models.PositiveIntegerField(default=0)
And perform the following query
Event.objects.annotate(
seats_remaining=F('seating') - Sum('reservations__seats').
)
Cheers,
Simon
[0]
https://docs.djangoproject.com/en/2.1/topics/db/aggregation/#generating-aggregates-for-each-item-in-a-queryset
Le jeudi 6 septembre 2018 07:42:36 UTC-4, [email protected] a écrit :
>
>
> QUESTION
>
> I have an application that will make on-line reservations for a series of
> weekly events. I would like to display the list of upcoming events in an
> html template with the number of remaining seats available in a single html
> page. I was able to create views to display the list of upcoming events and
> another view to display the number of remaining seats available but I am
> unable to figure out how to nest the two into a single view. Example
> below...
>
> HTML OUTPUT
>
> Event Title Week 1 - x amount of seats remaining for this event
>
> Event Title Week 2 - x amount of seats remainign for this event
>
> Event Title Week 3 - x amount of seats remaining for this event
>
> and so on ....
>
> MODELS
>
> class Events(models.Model):
> event_date = models.DateField(auto_now_add=False)
> event_time = models.TimeField(auto_now_add=False)
> event_type = models.CharField(max_length=20, choices=EVENT_TYPE)
> seating = models.IntegerField(default=0)
> title = models.CharField(max_length=200)
> description = models.TextField()
> menu = models.TextField()
> price = models.DecimalField(max_digits=6, decimal_places=2)
> publish = models.CharField(max_length=1, choices=PUBLISH_CHOICE)
>
> def __int__(self):
> return self.title
>
> class Reservations(models.Model):
> user_id = models.IntegerField(default=0)
> event_id = models.IntegerField(default=0)
> reservations = models.IntegerField(default=0)
>
> def __int__(self):
> return self.event
>
>
> VIEWS
>
> def events_view(request):
>
> events=Events.objects.filter(publish='Y').filter(event_date__gte=datetime.now()).order_by('event_date')
>
> reservation_count = Reservations.objects.aggregate(Sum('reservations'))
>
> return render(request, 'restaurant/events.html',{"events":events,
> "reservation_count":reservation_count, })
>
> def make_reservation_view(request, pk):
> event = Events.objects.get(id=pk)
> seating_available = Events.objects.get(id=pk)
> seating_available = seating_available.seating
> reservation_count =
> Reservations.objects.filter(event_id=pk).aggregate(res_sum=Sum('reservations'))
> res = reservation_count['res_sum']
> seats_remaining = seating_available - res
>
> return render(request, 'restaurant/make_reservation.html',
> {"event":event, \
>
> "seats_remaining":seats_remaining,})
>
>
>
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