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?

解决方案

OneToOneField(SomeModel) 和 ForeignKey(SomeModel, unique=True) 之间的差异，如Django 权威指南:

<块引用>

OneToOneField

一对一的关系.从概念上讲，这类似于带有 unique=True 的 ForeignKey，但反向"不相同.关系的一侧将直接返回单个对象.

与 OneToOneField 相比，反向"关系，一个 ForeignKey 反向"；关系返回一个 QuerySet.

示例

例如，如果我们有以下两个模型(完整模型代码如下):

1. Car 模型使用 OneToOneField(Engine)
2. Car2 模型使用 ForeignKey(Engine2, unique=True)

从 python manage.py shell 中执行以下内容:

OneToOneField 示例

<预><代码>>>>从 testapp.models 导入汽车，引擎>>>c = Car.objects.get(name='奥迪')>>>e = Engine.objects.get(name='Diesel')>>>电动汽车<汽车:奥迪>

ForeignKey with unique=True 示例

<预><代码>>>>从 testapp.models 导入 Car2, Engine2>>>c2 = Car2.objects.get(name='马自达')>>>e2 = Engine2.objects.get(name='Wankel')>>>e2.car2_set.all()[<Car2:马自达>]

型号代码

from django.db 导入模型类引擎(模型.模型):名称 = 模型.CharField(max_length=25)def __unicode__(self):返回 self.name类汽车(模型.模型):名称 = 模型.CharField(max_length=25)引擎 = 模型.OneToOneField(引擎)def __unicode__(self):返回 self.name类 Engine2(models.Model):名称 = 模型.CharField(max_length=25)def __unicode__(self):返回 self.name类 Car2(models.Model):名称 = 模型.CharField(max_length=25)引擎=models.ForeignKey(Engine2, unique=True, on_delete=models.CASCADE)def __unicode__(self):返回 self.name

What's the difference between Django OneToOneField and ForeignKey?

解决方案

Differences between OneToOneField(SomeModel) and ForeignKey(SomeModel, unique=True) as stated in The Definitive Guide to Django:

OneToOneField

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.

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

Example

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

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

From within python manage.py shell execute the following:

OneToOneField Example

>>> 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 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, on_delete=models.CASCADE)

    def __unicode__(self):
        return self.name

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