Django / Postgres按汇总分组

Question

I've have an issue regarding queries with a group by clause. Lets assume I have the following Django-Model:

class SomeModel(models.Model):
    date = models.DateField()
    value = models.FloatField()
    relation = models.ForeignKey('OtherModel')

If I want to do a query where I group SomeModel instances by OtherModel and annotate the latest date:

SomeModel.objects.values('relation').annotate(Max('date'))

This is all great, but as soon as I want to add a filter on the already annotated queryset I am getting nowhere:

SomeModel.objects.values('relation').annotate(Max('date')).filter(value__gt=0)

This would indeed filter out all the value != 0, however I only want it after the annotations took place. If the latest date of a relation has the value 0, I want it to be filtered out!

Answer 1

You need to add the value in the annotate filed and then you can filter over it. Your ORM query becomes

SomeModel.objects.values('relation').annotate(Max('date'), value=F('value')).filter(value__gt=0)

This should give the value you require