Can anyone help out with the following aggregation clause? I have an
invoice and invoice_item models as shown.
class Invoice(models.Model):
customer = models.ForeignKey(Customer)
payments_received = models.FloatField(default=0)
class Invoice_Item(models.Model):
invoice = models.ForeignKey('Invoice')
sub_total = models.DecimalField(blank=True, null=True,
max_digits=9, decimal_places=2)
I create one invoice with 2 items
i = Invoice(customer=c, payments_received=260)
i.save()
it = Invoice_Item(invoice=1, sub_total=200)
it.save()
it = Invoice_Item(invoice=1, sub_total=60)
it.save()
When performing an aggregate with one Sum the Sum of payments_received
field is correct
>>> account_balance =
>>> Invoice.objects.filter(customer=c).aggregate(Sum('payments_received'))
>>> account_balance
{'payments_received__sum': 260.0}
However when I add an additional item to the aggregate clause the
payments_received is doubled.
>>> account_balance =
>>> Invoice.objects.filter(customer=c).aggregate(Sum('invoice_item__sub_total'),
>>> Sum('payments_received'))
>>> account_balance
{'payments_received__sum': 520.0, 'invoice_item__sub_total__sum':
Decimal("260.00")}
I expected the payments_received sum to always stay the same, is my
understanding of aggregation flawed?
Paddy
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