django OneToOneField和ForeignKey有什么区别？ [英] What's the difference between django OneToOneField and ForeignKey?

问题描述

django OneToOneField和ForeignKey有什么区别？

What's the difference between django OneToOneField and ForeignKey?

推荐答案

请小心，意识到 OneToOneField（SomeModel）和 ForeignKey（SomeModel，unique = True）。如 Django的最终指南 ：

Be careful to realize that there are some differences between OneToOneField(SomeModel) and ForeignKey(SomeModel, unique=True). As stated in The Definitive Guide to Django:

OneToOneField

一对一的关系在概念上，这类似于 ForeignKey 与 unique = True ，但关系的反向一方将直接返回单个对象。

A one-to-one relationship. Conceptually, this is similar to a ForeignKey with unique=True, but the "reverse" side of the relation will directly return a single object.

与 OneToOneField 反向关系相反，一个 ForeignKey reverse关系返回一个 QuerySet 。

In contrast to the OneToOneField "reverse" relation, a ForeignKey "reverse" relation returns a QuerySet.

例如，如果我们有以下两个模型（下面是完整的模型代码）：

For example, if we have the following two models (full model code below):

1. 汽车模型使用 OneToOneField（Engine）


2. Car2 模型使用 ForeignKey（Engine2，unique = True）

1. Car model uses OneToOneField(Engine)
2. Car2 model uses ForeignKey(Engine2, unique=True)

从 python manage.py shell 执行以下操作：

>>> from testapp.models import Car, Engine
>>> c = Car.objects.get(name='Audi')
>>> e = Engine.objects.get(name='Diesel')
>>> e.car
<Car: Audi>

ForeignKey with unique = True 示例

ForeignKey with unique=True Example

>>> from testapp.models import Car2, Engine2
>>> c2 = Car2.objects.get(name='Mazda')
>>> e2 = Engine2.objects.get(name='Wankel')
>>> e2.car2_set.all()
[<Car2: Mazda>]

Model Code

from django.db import models

class Engine(models.Model):
    name = models.CharField(max_length=25)

    def __unicode__(self):
        return self.name

class Car(models.Model):
    name = models.CharField(max_length=25)
    engine = models.OneToOneField(Engine)

    def __unicode__(self):
        return self.name

class Engine2(models.Model):
    name = models.CharField(max_length=25)

    def __unicode__(self):
        return self.name

class Car2(models.Model):
    name = models.CharField(max_length=25)
    engine = models.ForeignKey(Engine2, unique=True)

    def __unicode__(self):
        return self.name

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