Re: Django Nested Query with Aggregate.Sum()

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, mab.mo...@gmail.com 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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