On Tue, Jun 23, 2009 at 2:36 AM, pr<crico...@gmail.com> wrote:
>
> Hi,
>
> I want to get total price (quantity*price) in this example for objest
> list (not one) of A class
>
> class A(models.Model)
> name = models.CharField(max_length=255)
>
> class B(models.Model)
> quantity = models.PositiveIntegerField()
> price = models.DecimalField(max_digits=10, decimal_places=2)
> a = models.ForeignKey(A)
>
> I try:
> A.objects.all().select_related().annotate(my_sum=Sum
> ('b__price*b__quantity'))
> but it doesn't work...
You can't currently annotate a computed expression onto a model (at
least, not using the annotate() clause). You can only annotate an
aggregate, which must be a Sum/max/min etc of a single field.
For the moment, if you want to do something like this, you will need
to look into using extra(select=...), or using custom SQL.
Annotating computed fields is something that I would like to add in
the future, but probably it probably won't get done until at least
Django v1.2, probably later (unless someone else volunteers to do the
work).
Yours,
Russ Magee %-)
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