自定义中间表（中介模型）

1 多对多关系中，第三张表的建立
-默认使用ManyToMany，自动创建
-使用中介模型
-即手动创建第三张表，又要使用好用的查询
-完全自己写第三张表

# 使用中介模型

class Author(models.Model):
nid = models.AutoField(primary_key=True)
name = models.CharField(max_length=32)
age = models.IntegerField()
author_detail = models.OneToOneField(to='AuthorDatail', to_field='nid', unique=True, on_delete=models.CASCADE)


class AuthorDatail(models.Model):
nid = models.AutoField(primary_key=True)
telephone = models.BigIntegerField()
birthday = models.DateField()
addr = models.CharField(max_length=64)


class Book(models.Model):
nid = models.AutoField(primary_key=True)
name = models.CharField(max_length=32)
price = models.DecimalField(max_digits=5, decimal_places=2)
publish_date = models.DateField()

publish = models.ForeignKey(to='Publish', to_field='nid', on_delete=models.CASCADE)
# 当前在哪个表中，元组中的第一个参数就是 表明_id
authors=models.ManyToManyField(to='Author',through='AuthorToBook',through_fields=('book_id','author_id'))
def __str__(self):
return self.name


class Publish(models.Model):
nid = models.AutoField(primary_key=True)
name = models.CharField(max_length=32)
city = models.CharField(max_length=32)
email = models.EmailField()


class AuthorToBook(models.Model):
nid = models.AutoField(primary_key=True)
book_id = models.ForeignKey(to=Book, to_field='nid', on_delete=models.CASCADE)
author_id = models.ForeignKey(to=Author, to_field='nid', on_delete=models.CASCADE)
date=models.DecimalField()

# s1.py

import os

if __name__ == '__main__':
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "day76.settings")
import django
django.setup()
from app01 import models

# 西游记这本书是lqz和egon写的
# book=models.Book.objects.get(pk=1)
# # book.authors.add(1,2) # 用不了了
# # 只能手动写
# models.AuthorToBook.objects.create(book_id_id=1,author_id_id=1)
# models.AuthorToBook.objects.create(book_id_id=1,author_id_id=2)

# 西游记这本书所有的作者

# book = models.Book.objects.get(pk=1)
# res=models.AuthorToBook.objects.filter(book_id=book)
# print(res)

# book = models.Book.objects.get(pk=1)
# print(book.authors.all())

# 西游记这本书是lqz和egon写的 add ,remove, clear,set
# 但是连表操作，book.authors这些都能用
book = models.Book.objects.get(pk=1)
book.authors.add(1,2) # 不能用了