{"title":"一对一关联","version":"4.2","locale":"zh-hans","docname":"topics/db/examples/one_to_one","url":"/zh-hans/4.2/topics/db/examples/one_to_one/","canonical":"https://djangodocs.dev/zh-hans/4.2/topics/db/examples/one_to_one/","summary":"要定义一对一关联，使用 OneToOneField 。 在本例中，一个 Place 可是一个 Restaurant : Code Copy from django.db import models class Place ( models . Model ): name = models . CharField (…","html":"

一对一关联Link to this heading#

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要定义一对一关联，使用 OneToOneField。

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在本例中，一个 Place 可是一个 Restaurant:

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Code
from django.db import models\n\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 f"{self.name} the place"\n\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\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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下面是可以使用PythonAPI工具执行的操作示例。

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创建几个 Places：

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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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创建一个餐厅。将“parent”对象作为此对象的主键传递：

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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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一个餐厅可以访问它的位置：

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Python console
>>> r.place\n<Place: Demon Dogs the place>\n
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一个地点可以访问它的餐厅，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 没有关联的餐厅：

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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.")\n...\nThere is no restaurant here.\n
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您还可以使用 hasattr 来避免需要捕获异常：

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Python console
>>> hasattr(p2, "restaurant")\nFalse\n
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使用赋值符号设置地点。由于地点是餐厅的主键，保存操作将创建一个新的餐厅：

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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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再次使用反向赋值方式设置地点：

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Python console
>>> p1.restaurant = r\n>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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请注意，在将对象分配给一对一关系之前，您必须先保存该对象。例如，使用未保存的 Place 创建一个 Restaurant 会引发 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() 返回的是餐厅，而不是地点。请注意，有两家餐厅 - Ace Hardware 餐厅是在调用 r.place = p2 时创建的：

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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() 返回所有地点，不管它们是否有餐厅：

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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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您可以使用 跨关系的查找 来查询模型：

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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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这也可以反过来做：

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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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如果你删除一个地方，它的餐馆将被删除（假设 OneToOneField 是用 on_delete 设置为 CASCADE 定义的，这是默认值）：

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Python console
>>> p2.delete()\n(2, {'one_to_one.Restaurant': 1, 'one_to_one.Place': 1})\n>>> Restaurant.objects.all()\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n
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在餐馆中添加一个服务员：

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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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查询服务员：

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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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