{"title":"One-to-one relationships","version":"2.1","locale":"zh-hans","docname":"topics/db/examples/one_to_one","url":"/zh-hans/2.1/topics/db/examples/one_to_one/","canonical":"https://djangodocs.dev/zh-hans/2.1/topics/db/examples/one_to_one/","summary":"To define a one-to-one relationship, use OneToOneField . In this example, a Place optionally can be a Restaurant : Code Copy from django.db import models class…","html":"

One-to-one relationshipsLink to this heading#

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To define a one-to-one relationship, use\nOneToOneField.

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In this example, a Place optionally can be a Restaurant:

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Code
from django.db import models\n\nclass Place(models.Model):\n    name = models.CharField(max_length=50)\n    address = models.CharField(max_length=80)\n\n    def __str__(self):\n        return "%s the place" % self.name\n\nclass Restaurant(models.Model):\n    place = models.OneToOneField(\n        Place,\n        on_delete=models.CASCADE,\n        primary_key=True,\n    )\n    serves_hot_dogs = models.BooleanField(default=False)\n    serves_pizza = models.BooleanField(default=False)\n\n    def __str__(self):\n        return "%s the restaurant" % self.place.name\n\nclass Waiter(models.Model):\n    restaurant = models.ForeignKey(Restaurant, on_delete=models.CASCADE)\n    name = models.CharField(max_length=50)\n\n    def __str__(self):\n        return "%s the waiter at %s" % (self.name, self.restaurant)\n
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What follows are examples of operations that can be performed using the Python\nAPI facilities.

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创建几个地方：

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Python console
>>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton')\n>>> p1.save()\n>>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland')\n>>> p2.save()\n
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创建一个餐馆，将“父”对象的ID传递为该对象的ID：

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Python console
>>> r = Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)\n>>> r.save()\n
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餐厅可进入其地点：

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Python console
>>> r.place\n<Place: Demon Dogs the place>\n
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一个可以进入餐厅的地方（如果有的话）：

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Python console
>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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p2没有关联餐厅：

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Python console
>>> from django.core.exceptions import ObjectDoesNotExist\n>>> try:\n>>>     p2.restaurant\n>>> except ObjectDoesNotExist:\n>>>     print("There is no restaurant here.")\nThere is no restaurant here.\n
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您还可以使用``hasattr`` 来避免例外捕获的需要：

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Python console
>>> hasattr(p2, 'restaurant')\nFalse\n
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使用赋值符号来设置地方。因为地方是餐厅的主键，保存将创建一个新的餐馆：

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Python console
>>> r.place = p2\n>>> r.save()\n>>> p2.restaurant\n<Restaurant: Ace Hardware the restaurant>\n>>> r.place\n<Place: Ace Hardware the place>\n
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再次设置地方，使用相反方向的赋值：

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Python console
>>> p1.restaurant = r\n>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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Note that you must save an object before it can be assigned to a one-to-one\nrelationship. For example, creating a Restaurant with unsaved Place\nraises ValueError:

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Python console
>>> p3 = Place(name='Demon Dogs', address='944 W. Fullerton')\n>>> Restaurant.objects.create(place=p3, serves_hot_dogs=True, serves_pizza=False)\nTraceback (most recent call last):\n...\nValueError: save() prohibited to prevent data loss due to unsaved related object 'place'.\n
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Restaurant.objects.all() just returns the Restaurants, not the Places. Note\nthat there are two restaurants - Ace Hardware the Restaurant was created in the\ncall to r.place = p2:

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Python console
>>> Restaurant.objects.all()\n<QuerySet [<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]>\n
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Place.objects.all() returns all Places, regardless of whether they have\nRestaurants:

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Python console
>>> Place.objects.order_by('name')\n<QuerySet [<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]>\n
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You can query the models using lookups across relationships:

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Python console
>>> Restaurant.objects.get(place=p1)\n<Restaurant: Demon Dogs the restaurant>\n>>> Restaurant.objects.get(place__pk=1)\n<Restaurant: Demon Dogs the restaurant>\n>>> Restaurant.objects.filter(place__name__startswith="Demon")\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n>>> Restaurant.objects.exclude(place__address__contains="Ashland")\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n
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This of course works in reverse:

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Python console
>>> Place.objects.get(pk=1)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant__place=p1)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant=r)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant__place__name__startswith="Demon")\n<Place: Demon Dogs the place>\n
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Add a Waiter to the Restaurant:

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Python console
>>> w = r.waiter_set.create(name='Joe')\n>>> w\n<Waiter: Joe the waiter at Demon Dogs the restaurant>\n
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Query the waiters:

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