Try this:
Process.objects.filter(exchange__input__unit__unit="kilogram")\
.annotate(sum_amount=Sum("exchange__amount"))\
.filter(sum_amount__gt=1)
On Fri, Jan 16, 2009 at 12:38 PM, Christopher Mutel <cmu...@gmail.com>
wrote:
>
> Following the general rule that no good deed goes unpunished, I have a
> question about complex aggregation / annotation or annotation across
> foreign keys.
>
> I have the following simplified model:
>
> class Unit(models.Model):
>unit = models.TextField()
>
> class Process(models.Model):
>process = models.TextField()
>unit = models.ForeignKey(Unit)
>
> class Exchange(models.Model):
>input = models.ForeignKey(Process)
>output = models.ForeignKey(Process)
>amount = models.FloatField()
>
> Is there a way for me to get a queryset for Process outputs which have
> a sum of inputs greater than one kilogram?
>
> You can do this (painfully) now by looping:
>
> foo = []
> for p in Process.objects.all():
>if sum(Exchange.objects.filter(ouput=p,
> input__unit__unit="kilogram").values_list('amount', flat=True)) > 1:
>foo.append(p)
>
> Sorry if this is a basic question, but I have been trying to figure it
> out for a while, and without success.
>
> -Chris
>
> >
>
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