Django query by foreign key

Question

I am learning Django, and I have this basic model:

from django.db import models

class Country(models.Model):
    name = models.CharField(max_length=255,)
    continent = models.ForeignKey('Continent')

class Continent(models.Model):
    name = models.CharField(max_length=255, unique = True)
    countries = ???

I want the Continent.countries attribute to return the matching countries, with continent-foreign key set to this continent. From Django docs I found that I should use foreign key, but the backward query is causing problems. I have experimented a few ways, but as a beginner I cant find the "correct" way of doing this. Any suggestions?

Answer 1

You don't need to create a countries attribute in Continent to establish a reverse relationship. You can find the Countries attached to each Continent by using the reverse ForeignKey relationship:

continent = Continent.objects.get(name='Asia')
countries = continent.country_set.all()

The country_set function is created by Django when you create a ForeignKey relationship between Country and Continent .

Answer 2

I agree with xyres . Also, you can define related_name in ForeignKey like:

continent = models.ForeignKey('Continent', related_name='countries')

so that, you can easily get countries in a continent:

continent.countries.all()

here, continent is object of the model Continent.