CODEWITHSUNDEEP
pythondjangodjango-querysetannotate
C.B.
C.B.

Reputation: 8326

Django max based on foreign key queryset

I would like to annotate a queryset based on a foreign key, i.e.

class A(models.Model):
    name = models.CharField(max_length=200)

class B(models.Model):
    value = models.IntegerField()
    a = models.ForeignKey(A)

I would like to annotate the B queryset with Max, but each Max being filtered to the a foreign key.

I have a feeling I would have to filter out the foreign key I wanted, and then annotate.

qs = B.objects.filter(a=some_specific_instance_of_A).annotate(max_value=Max('value'))

But would like to do something like

qs = B.objects.annotate(max_value=Max('value'), key='a')

Upvotes: 0

Views: 1695

Answers (1)

Peter DeGlopper
Peter DeGlopper

Reputation: 37319

Use a values clause to group prior to annotating.

qs = B.objects.values('a').annotate(max_value=Max('value'))

Upvotes: 1

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