One to many queries in Django

Question

This is my City object:

class City(Base):
    country = models.ForeignKey(Country, on_delete=models.CASCADE)
    name = models.CharField(max_length=255)
    latitude = models.FloatField()
    longitude = models.FloatField()

And this is my user:

class User(AbstractBaseUser, PermissionsMixin, Base):
    username = models.CharField(db_index=True, null=False, unique=True, max_length=255)
    mobile = models.CharField(db_index=True, max_length=100, null=True, unique=True)
    city = models.ForeignKey(City, on_delete=models.CASCADE, null=True)

How do I query cities which have more than 1 user?

Daniel Roseman · Accepted Answer · 2019-03-14 20:32:24Z

2

Use annotations:

from django.db.models import Count
City.objects.annotate(user_count=Count("user")).filter(user_count__gt=1)

edited Mar 14, 2019 at 20:32

answered Mar 14, 2019 at 20:09

Daniel Roseman

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5 Comments

Melissa Stewart Over a year ago

Does this return the count of cities with more than one user?

Daniel Roseman Over a year ago

No, it returns the cities, not the count.

Melissa Stewart Over a year ago

This gives me a syntax error, is this complete code?

Daniel Roseman Over a year ago

Sorry, missed a close parenthesis, try it now.

Melissa Stewart Over a year ago

Yup works now, I'm using it as city_count = City.objects.annotate(user_count=Count("user").filter(user_count__gt=1).count()

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