Django ORM 关系管理对象的创建

• 第一种方法自动创建第三张表

from django.db import models
class Book(models.Model):
title = models.CharField(max_length=32)
pub = models.ForeignKey('Publisher', on_delete=models.CASCADE)

class Author(models.Model):
name = models.CharField(max_length=32)
books = models.ManyToManyField('Book')  # 不会生成字段  生成第三张表 可以set等方法

• 第二种方法手动创建第三张表

class Book(models.Model):
title = models.CharField(max_length=32, unique=True)

class Author(models.Model):
name = models.CharField(max_length=32)

class AuthorBook(models.Model):
book = models.ForeignKey('Book',on_delete=models.CASCADE)
author = models.ForeignKey('Author',on_delete=models.CASCADE)
date = models.CharField(max_length=32)
# 第三张表不能够使用 set方法

• 第三种半自动创建

class Book(models.Model):
title = models.CharField(max_length=32, unique=True)

class Author(models.Model):
name = models.CharField(max_length=32)
books = models.ManyToManyField('Book',through='AuthorBook')  # 只用django提供的查询方法  不用创建表 用用户创建的表AuthorBook

class AuthorBook(models.Model):
book = models.ForeignKey('Book',on_delete=models.CASCADE)
author = models.ForeignKey('Author',on_delete=models.CASCADE)
date = models.CharField(max_length=32)

class Book(models.Model):
title = models.CharField(max_length=32, unique=True)

class Author(models.Model):
name = models.CharField(max_length=32)
books = models.ManyToManyField('Book',through='AuthorBook',through_fields=['author','book'])  # 只用django提供的查询方法  不用创建表 用用户创建的表AuthorBook

class AuthorBook(models.Model):
book = models.ForeignKey('Book',on_delete=models.CASCADE,null=True)
author = models.ForeignKey('Author',on_delete=models.CASCADE,related_name='x1',null=True)
tuiianren = models.ForeignKey('Author',on_delete=models.CASCADE,related_name='x2',null=True)
date = models.CharField(max_length=32)

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