django中model的symmetrical参数

最新推荐文章于 2023-06-29 14:52:52 发布

原创最新推荐文章于 2023-06-29 14:52:52 发布 · 989 阅读

1 ·

CC 4.0 BY-SA版权

文章标签：

#python #django

Python/Django 专栏收录该内容

25 篇文章

订阅专栏

本文详细解析了Django中M2M字段的symmetrical参数，解释了其在自引用场景下的作用，即控制多对多关系是否为对称。通过对Person模型的示例，阐述了设置symmetrical为False时，如何实现非对称的多对多关系。

M2M中symmetrical参数

需求
- 说明

需求

朋友关系，需要M2M自身，代码如下：

class Person(models.Model):
    friends=(models.ManyToManyField("self", symmetrical=False)

说明

官方明确的说了，只有当M2M引用self时，symmetrical才起作用。用来标注是否创建反向关系数据。之前没有碰到过这种需求，就不知道这么个参数。

今天碰到了就做个记录。

官方原始说明：

Only used in the definition of ManyToManyFields on self. Consider the following model:
from django.db import models
class Person(models.Model):
   friends = models.ManyToManyField("self")
When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn’t add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical – that is, if I am your friend, then you are my friend.
If you do not want symmetry in many-to-many relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToManyField relationships to be non-symmetrical.