#

## Django documentation

# 10. One-to-one relationships

To define a one-to-one relationship, use `OneToOneField()`.

In this example, a `Place` optionally can be a `Restaurant`.

## 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()

## Comments

### ianm August 12, 2005 at 1:27 p.m.

Is there a way to use the edit_inline admin feature? I cannot find any examples and the standard ForeignKey example does not work for me.

## Post a comment

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