Question

I have to implement two models in a django project –> Country and Continent.
It is possible to import all information about countries and continents from an XML file that populates the database with these two tables.

I’ve implemented them in this way

from django.db import models

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

        class Meta:
            ordering = ['name']

    class Country(models.Model):
        name = models.CharField(max_length=255)
        capital = models.CharField(max_length=255)
        code = models.CharField(max_length=255, unique=True)
        population = models.IntegerField(default=0)
        area = models.IntegerField(default=0)
        continent = models.ForeignKey(Continent)

        class Meta:
            ordering = ['name']

You can see a ? mark in Continent.countries because I don’t understand how to implement it. The problem is: “Countries of a continent should be accessible through attribute countries of class Continent”

This means that it is possible to do this:

from MyApplication.model import Country, Continent
europe = Continent.object.get(code=u'eu')
finland = europe.countries.get(code=u'fi')

I’ve tried models.ForeignKey, but it doesn’t work.
It says that “Nonetype object doesn’t have any get method”
Can anyone help me please?

Thanks

Answer 1

Django does not support one to many directly, instead you can use the reverse of one-to-one relation to get a one-to-many relation.

So, go ahead with the other approach of using many to one by adding foreign key inside the country relating to continent. Now, you have a one-to-one from country to continent. Next, do a reverse query from Continent‘s object to get the desired relation. Take a look:

class Continent(models.Model):
    ...

class Country(models.Model):
    ...
    continent = models.ForeignKey(Continent, related_name="countries")
    ...

europe = Continent.object.get(code=u'eu')
finland = europe.countries.get(code=u'fi')