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Django模型中的OneToOneField和ForeignKey有什么区别?

时间:2019-09-21 17:18:11      阅读:132      评论:0      收藏:0      [点我收藏+]

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说是ForeignKey是one-to-many的,并举了一个车的例子:

有两个配件表,一个是车轮表,另一个是引擎表。两个表都有一个car字段,表示该配件对应的车。
对于车轮来说,多个对应一个car的情况很正常,所以car字段应该用ForeignKey来表示。
对于引擎来说,一个引擎只可能对应一个car,所以必须用OneToOneField。

OneToOneField(someModel) 可以理解为 ForeignKey(SomeModel, unique=True)。

两者的反向查询是有差别的:

ForeignKey反向查询返回的是一个列表(一个车有多个轮子)。

OneToOneField反向查询返回的是一个模型示例(因为一对一关系)。

另外的补充说明:

Be careful to realize that there are some differences between OneToOneField(SomeModel) andForeignKey(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 aQuerySet.

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

Car model uses OneToOneField(Engine)
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)

引自redice,侵删

Django模型中的OneToOneField和ForeignKey有什么区别?

标签:uniq   tap   diff   har   说明   mem   from   nic   class   

原文地址:https://www.cnblogs.com/luowenConnor/p/11563573.html

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