Django query multiple summed values - django

Question

I have two tables:
Ticket Table
id paid_with_tax location
1 5 A
2 6 B
3 7 B
TicketAdjustment Table
id ticket_id value_with_tax
1 1 2
2 1 1
3 1 2
4 1 3
5 2 5
The query I use:
Ticket.objects.all().annotate(
paid_amount=Sum(
F('paid_with_tax') +
Coalesce(F('ticketadjustment__value_with_tax'), 0)
)
).values(
'paid_amount', 'location'
).annotate(
Count('id)
)
the query would return the following:
[
{
id__count: 6,
paid_amount__sum: 28,
location: A
},
{
id__count: 2,
paid_amount__sum: 18,
location: B
},
]
but the above is incorrect since the Ticket Table id=1 values are duplicated by the TicketAdjustment Table values.
how can i get the query to sum the TicketAdjustment Table values before adding them up.
Some constraints:
- the order of the calls would ideally stay the same, as I have a function which returns the queryset to be filtered thurther
The final result should look as followins:
[
{
id__count: 1,
paid_amount__sum: 13,
location: A
},
{
id__count: 2,
paid_amount__sum: 18,
location: B
},
]
models.py:
class Ticket(models.Model):
paid_with_tax = models.DecimalField(max_digits=6, decimal_places=4)
location = models.ForeignKey(Location)
class TicketAdjustment(models.Model):
value_with_tax = models.DecimalField(max_digits=6, decimal_places=4)
ticket = models.ForeignKey(Ticket)

Answer 1

As I understand this aggregation can not be done even using raw sql query. Because the result of joining Ticket with TicketAdjustment will be like:
So, we can't just sum all value_with_tax related to some ticket with paid_with_tax and group that by location.
I couldn't find solution to perform this in one sql query. But I have found how to perform this in two queries:
tickets = Ticket.objects.values(
'location',
).annotate(
count=Count('id', distinct=True),
paid_amount=Sum('paid_with_tax')
)
# <QuerySet [
# {'paid_amount': 5, 'count': 1, 'location': 'A'},
# {'paid_amount': 13, 'count': 2, 'location': 'B'}
# ]>
adjustments = TicketAdjustment.objects.annotate(
location=F('ticket__location'))
.values(
'location',
).annotate(
paid_amount=Sum('value_with_tax')
)
# <QuerySet [
# {'paid_amount': 5, 'location': 'B'},
# {'paid_amount': 8, 'location': 'A'}
# ]>
def find_paid_amount_for_list_and_location(l, location):
for item in l:
if item['location'] == location:
return item['paid_amount'] or 0
for obj in tickets:
paid = find_paid_amount_for_list_and_location(adjustments, obj['location'])
obj['paid_amount'] += paid
tickets
# [
# {'location': 'A', 'paid_amount': 13, 'count': 1},
# {'location': 'B', 'paid_amount': 18, 'count': 2}
# ]
But this is not super efficient solution, and I think that you should create new table for locations and just have FK to that table? In this case you will able to perform these calculations in one query on db side.