CODEWITHSUNDEEP
djangodjango-modelsdjango-queryset
Garvit Jain
Garvit Jain

Reputation: 635

Django count nested m2m objects

I have 3 models - 

class A(models.Model):
    ...
    b = models.ManyToManyField(B, related_name="related_a")

class B(models.Model):
    ...

class Entries(models.Model):
    ...
    b = models.ForeignKey(B, related_name="entries")

I need to loop over all A objects and show the count of entries for each b in A, along with other fields in A. What would be the most efficient way to do it?

Upvotes: 1

Views: 444

Answers (1)

Endre Both
Endre Both

Reputation: 5730

You can get it done in 2 queries:

from django.db.models import Count, Prefetch

qs = B.objects.annotate(entry_count=Count('entries'))
a_list = A.objects.prefetch_related(Prefetch('b', queryset=qs))

I hope I've got all related names right. You can access the counts like this:

for a in a_list:
    for b_item in a.b:
        print(b_item.entry_count)

Upvotes: 1

Related Questions