Hubungan satu-ke-satuΒΆ

Untuk menentukan hubungan satu-ke-satu, gunakan OneToOneField.

Dalam contoh ini, sebuah pilihan Place dapat menjadi sebuah Restaurant:

from django.db import models

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

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

class Restaurant(models.Model):
    place = models.OneToOneField(
        Place,
        on_delete=models.CASCADE,
        primary_key=True,
    )
    serves_hot_dogs = models.BooleanField(default=False)
    serves_pizza = models.BooleanField(default=False)

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

class Waiter(models.Model):
    restaurant = models.ForeignKey(Restaurant, on_delete=models.CASCADE)
    name = models.CharField(max_length=50)

    def __str__(self):
        return "%s the waiter at %s" % (self.name, self.restaurant)

Apa yang mengikuti adalah contoh-contoh dari tindakan yang dapat dilakukan menggunakan fasilitas API Python.

Buat sepasang Place:

>>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton')
>>> p1.save()
>>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland')
>>> p2.save()

Create a Restaurant. Pass the "parent" object as this object's primary key:

>>> r = Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)
>>> r.save()

Sebuah Restaurant dapat mengakses tempatnya:

>>> r.place
<Place: Demon Dogs the place>

Sebuah Place dapat mengakses restorannya, jika tersedia:

>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>

p2 tidak mempunyai restoran terkait:

>>> from django.core.exceptions import ObjectDoesNotExist
>>> try:
>>>     p2.restaurant
>>> except ObjectDoesNotExist:
>>>     print("There is no restaurant here.")
There is no restaurant here.

Anda dapat juga menggunakan hasattr untuk menghindari kebutuhan untuk menangkap pengecualian:

>>> hasattr(p2, 'restaurant')
False

Setel tempat menggunakan penugasan catatan. Karena tempat adalah primary key pada Restaurant, penyimpanan akan membuat sebuah restoran baru:

>>> r.place = p2
>>> r.save()
>>> p2.restaurant
<Restaurant: Ace Hardware the restaurant>
>>> r.place
<Place: Ace Hardware the place>

Setel tempat kembali lagi, menggunakan penugasan dalam membalikkan arah:

>>> p1.restaurant = r
>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>

Catat bahwa anda harus menyimpan sebuah obyek sebelum itu dapat diberikan ke hubungan one-to-one. Sebagai contoh, membuat Restaurant dengan Place tidak disimpan memunculkan ValueError:

>>> p3 = Place(name='Demon Dogs', address='944 W. Fullerton')
>>> Restaurant.objects.create(place=p3, serves_hot_dogs=True, serves_pizza=False)
Traceback (most recent call last):
...
ValueError: save() prohibited to prevent data loss due to unsaved related object 'place'.

Restaurant.objects.all() returns the Restaurants, not the Places. Note that there are two restaurants - Ace Hardware the Restaurant was created in the call to r.place = p2:

>>> Restaurant.objects.all()
<QuerySet [<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]>

Place.objects.all() mengembalikan semua Places, tanpa memperhatikan apakah mereka mempunyai Restaurants:

>>> Place.objects.order_by('name')
<QuerySet [<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]>

Anda dapat meminta model menggunakan lookups across relationships:

>>> Restaurant.objects.get(place=p1)
<Restaurant: Demon Dogs the restaurant>
>>> Restaurant.objects.get(place__pk=1)
<Restaurant: Demon Dogs the restaurant>
>>> Restaurant.objects.filter(place__name__startswith="Demon")
<QuerySet [<Restaurant: Demon Dogs the restaurant>]>
>>> Restaurant.objects.exclude(place__address__contains="Ashland")
<QuerySet [<Restaurant: Demon Dogs the restaurant>]>

This also works in reverse:

>>> Place.objects.get(pk=1)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant__place=p1)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant=r)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant__place__name__startswith="Demon")
<Place: Demon Dogs the place>

Tambah Waiter ke Restaurant:

>>> w = r.waiter_set.create(name='Joe')
>>> w
<Waiter: Joe the waiter at Demon Dogs the restaurant>

Meminta pelayan:

>>> Waiter.objects.filter(restaurant__place=p1)
<QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]>
>>> Waiter.objects.filter(restaurant__place__name__startswith="Demon")
<QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]>