try making two separate annotates: one for count and one for the case-when
qs.values('make')
.annotate(count = Count('model', distinct = True))
.annotate(Case(When(count__gt = 1, then='yes', output_field=CharField())
Basically, you need to transform the count annotation into something django
can use its lookup syntax with.
On Wednesday, July 4, 2018 at 6:37:27 PM UTC-4, Magnus Ljungkrantz wrote:
>
>
> To give you simplest possible example of my problem, let us say we have a
> table holding data about physical cars. It has many fields but "make" and
> "model" are two of them.
>
> The following SQL will group on make and let me know with "yes "or "no"
> whether there is more than one model within each group of cars of a
> specific make.
>
> SELECT
> make,
> CASE WHEN COUNT(DISTINCT model) > 1 THEN 'yes' ELSE 'no' END AS
> more_than_one_model
> FROM myapp_car
> GROUP BY make
>
> I know how to group on make and count unique models s
>
> qs = Car.objects.all().values('make').annotate(model_count=Count('model',
> distinct=True))
>
> but I cannot figure out how to produce "yes" or "no" result depending on
> the outcome of a Count(). The following
>
> qs = qs.values('make').annotate(
> more_than_one_model=Case(
> When(Count('model', distinct=True) > 1, then='yes'),
> default='no'
> ),
> output_field=models.CharField()
> )
>
>
> gives me an exception saying "'>' not supported between instances of 'Count'
> and 'int'".
>
>
> Any ideas how to accomplish this?
>
>
>
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