Hi Erik,
I tried your solution but there are some issues:
.filter(date_created=Max('a__b__date_created')) - this is throwing error
saying not proper use of group function.
If I remove the above, the result isn't correct where when I go through
each 'a' in the result, associated latest B.text isn't always 'ABCD' - if
there are multiple instances of B associated with an instance of A and one
of the instances of B has text='ABCD' (might not be the latest
date_created), that instance of B is also there in the query result.
Thanks.
On Tuesday, August 30, 2016 at 3:59:20 PM UTC+5:30, Erik Cederstrand wrote:
>
>
> > Den 30. aug. 2016 kl. 11.20 skrev Erik Cederstrand <
> erik+...@cederstrand.dk <javascript:>>:
> >
> > I'm not even sure that's possible to express in SQL, but it would
> probably be quite convoluted if it is. Here's an easier-to-understand
> solution:
> >
> > res = set()
> > for b in
> B.objects.all().select_related('a').annotate(Max('date_created')):
> > if b.date_created != b.date_created__max:
> > continue
> > if b.text != 'ABCD':
> > continue
> > res.add(a)
>
> I did some more experimenting. I think this actually does what you want:
>
> res = [
> b.a for b in B.objects
> .filter(date_created=Max('a__b__date_created'))
> .annotate(Max('a__b__date_created'))
> .filter(text='ABCD')
> .select_related('a')
> ]
>
> which you can rewrite as:
>
> A.objects.filter(
> b__in=B.objects
> .filter(date_created=Max('a__b__date_created'))
> .annotate(Max('a__b__date_created'))
> .filter(text='ABCD')
> )
>
> Erik
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