要定义一对一关联，使用 OneToOneField。
在本例中，一个 Place 是一个 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)
下面是可以使用PythonAPI工具执行的操作示例。
创建几个 Place：
>>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton')
>>> p1.save()
>>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland')
>>> p2.save()
创建一个 Restaurant。传递父对象作为该对象的主键：
>>> r = Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)
>>> r.save()
Restaurant可以获取所在地
>>> r.place
<Place: Demon Dogs the place>
Place可以访问关联的Restaurant（如果有的话）：
>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>
p2 没有关联餐厅：
>>> from django.core.exceptions import ObjectDoesNotExist
>>> try:
>>> p2.restaurant
>>> except ObjectDoesNotExist:
>>> print("There is no restaurant here.")
There is no restaurant here.
您还可以使用 hasattr 来免除异常捕获：
>>> hasattr(p2, 'restaurant')
False
使用赋值符号来设置Place。因为Place是Restaurant的主键，保存将创建一个新的Restaurant：
>>> r.place = p2
>>> r.save()
>>> p2.restaurant
<Restaurant: Ace Hardware the restaurant>
>>> r.place
<Place: Ace Hardware the place>
再次设置Place，使用相反方向的赋值：
>>> p1.restaurant = r
>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>
注意，将某个对象指定给一个一对一关联关系之前，必须先保存它。例如，利用未保存的 Place 创建一个 Restaurant 会抛出 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() 返回所有Restaurant，而不是Place。注意，这里有两个Restaurant —— Ace Hardware the Restaurant 是在调用 r.place = p2 时创建的：
>>> Restaurant.objects.all()
<QuerySet [<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]>
Place.objects.all() 返回所有的 Place，不管其是否有关联Restaurant:
>>> Place.objects.order_by('name')
<QuerySet [<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]> 你可以用 跨关联查询 查询这些模型:
>>> 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>]>
反向查询也是可以的:
>>> 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>
为Restaurant添加一个Waiter:
>>> w = r.waiter_set.create(name='Joe')
>>> w
<Waiter: Joe the waiter at Demon Dogs the restaurant>
查询Waiter:
>>> 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>]>