10. One-to-one relationships

Model source code

from django.core import meta

class Place(meta.Model):
    name = meta.CharField(maxlength=50)
    address = meta.CharField(maxlength=80)

    def __repr__(self):
        return "%s the place" % self.name

class Restaurant(meta.Model):
    place = meta.OneToOneField(Place)
    serves_hot_dogs = meta.BooleanField()
    serves_pizza = meta.BooleanField()

    def __repr__(self):
        return "%s the restaurant" % self.get_place().name

class Waiter(meta.Model):
    restaurant = meta.ForeignKey(Restaurant)
    name = meta.CharField(maxlength=50)

    def __repr__(self):
        return "%s the waiter at %r" % (self.name, self.get_restaurant())

API reference

Place objects have the following methods:

• delete()
• get_restaurant()
• save()

Restaurant objects have the following methods:

• add_waiter()
• delete()
• get_place()
• get_waiter()
• get_waiter_count()
• get_waiter_list()
• save()

Waiter objects have the following methods:

• delete()
• get_restaurant()
• save()

Sample API usage

This sample code assumes the above models have been saved in a file examplemodel.py.

>>> from django.models.examplemodel import places, restaurants, waiters

# Create a couple of Places.
>>> p1 = places.Place(name='Demon Dogs', address='944 W. Fullerton')
>>> p1.save()
>>> p2 = places.Place(name='Ace Hardware', address='1013 N. Ashland')
>>> p2.save()

# Create a Restaurant. Pass the ID of the "parent" object as this object's ID.
>>> r = restaurants.Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)
>>> r.save()

# A Restaurant can access its place.
>>> r.get_place()
Demon Dogs the place

# A Place can access its restaurant, if available.
>>> p1.get_restaurant()
Demon Dogs the restaurant

# p2 doesn't have an associated restaurant.
>>> p2.get_restaurant()
Traceback (most recent call last):
    ...
RestaurantDoesNotExist: Restaurant does not exist for {'place__id__exact': ...}

# restaurants.get_list() just returns the Restaurants, not the Places.
>>> restaurants.get_list()
[Demon Dogs the restaurant]

# places.get_list() returns all Places, regardless of whether they have
# Restaurants.
>>> places.get_list(order_by=['name'])
[Ace Hardware the place, Demon Dogs the place]

>>> restaurants.get_object(place__id__exact=1)
Demon Dogs the restaurant
>>> restaurants.get_object(pk=1)
Demon Dogs the restaurant

# Add a Waiter to the Restaurant.
>>> w = r.add_waiter(name='Joe')
>>> w.save()
>>> w
Joe the waiter at Demon Dogs the restaurant

>>> r = restaurants.get_object(pk=1)
>>> r.delete()