Django OneToOneField和ForeignKey的区别

根据Django官方文档介绍:

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.


OneToOneField与ForeignKey加上unique=True效果基本一样，但是用OneToOneField反向关联会直接返回对象。

相反地，使用ForeignKey, 反向关联后会返回QuerySet。

例子：

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

在python manage.py shell里输入:

>>> from testapp.models import Car, Engine
>>> c = Car.objects.get(name='Audi')
>>> e = Engine.objects.get(name='Diesel')
>>> e.car   # OneToOneField的反向关联属性如果没有写relate_name, 则是对方类名的小写

>>> from testapp.models import Car2, Engine2
>>> c2 = Car2.objects.get(name='Mazda')
>>> e2 = Engine2.objects.get(name='Wankel')
>>> e2.car2_set.all()   # OneToOneField的反向关联属性如果没有写relate_name, 则是对方类名的小写_set
[]