Roland,
Instead of using annotate, could you just add the avg_days_instock
field as another key in the select argument to extra?
Ian
On Tue, May 18, 2010 at 9:03 PM, Roland van Laar <rol...@micite.net> wrote:
> Hello,
>
> Question: How do I calculate the Average of a calculated field.
>
> My (simplified) models.py:
>
> Manufacturer(models.Model):
> name = models.CharField(length=100)
>
> Product(models.Model):
> name = models.CharField(length=100)
>
> Items(models.Model):
> manufacturer = models.Foreignkey(Manufacturer)
> product = models.ForeignKey(Product)
> bought_date = models.DateField()
> sold_date = models.DateField(null=True, blank=True)
>
> On these models I want to calculate the number of days an item was in stock
> on a given date:
>
> qs = Items.objects.all().extra(select= \
> {'days_in_stock': "'%s' - transactie_datum_inkomend + 1" %
> (given_date.isoformat())})
>
> And then I want to know the average number of days all the items selected on
> manufacturer and product.
>
> qs.values('manufacturer', 'product)
> qs.annotate(Count('manufacturer'), avg_days_instock=Avg('days_in_stock'))
>
> The annotate fails because 'days_in_stock' is not a valid field:
> FieldError: Cannot resolve keyword 'days_in_stock' into field. Choices are:
> manufacturer, product, bought_date, sold_date
>
> How can I calculate the average of the days_in_stock?
>
> Thanks,
>
> Roland van Laar
>
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django users" group.
> To post to this group, send email to django-us...@googlegroups.com.
> To unsubscribe from this group, send email to
> django-users+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/django-users?hl=en.
>
>
--
=======================================
株式会社ビープラウド イアン・ルイス
〒150-0021
東京都渋谷区恵比寿西2-3-2 NSビル6階
email: ianmle...@beproud.jp
TEL:03-6416-9836
FAX:03-6416-9837
http://www.beproud.jp/
=======================================
--
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-us...@googlegroups.com.
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en.
