Django之modles 多对多创建第三张表

class Book(models.Model):
    title = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=8, decimal_places=2)
    authors = models.ManyToManyField(to=‘Author‘)
    

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

class Book(models.Model):
    title = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=8, decimal_places=2)


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

# 纯手动创建第三张表
class Book2Author(models.Model):
    Book = models.ForeignKey(to=‘Book‘)
    Author = models.ForeignKey(to=‘Author‘)
    # 基于第一种没有办法拓展我们第三张表中的字段 纯自动固定只有我们的Book和Author 拓展性极差
    info = models.CharField(max_length=64)

import os
import sys

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "test_22.settings")
    import django
    django.setup()

    from app01 import models

    # res = models.Book.objects.filter(pk=1).values(‘author__name‘)
    # print(res)  # 基于双下划线反向表名也不行了

    book_obj = models.Book.objects.filter(pk=1).first()
    print(book_obj.author__set.all())  # AttributeError: ‘NoneType‘ object has no attribute ‘author__set

    # 基于对象单向表名小写_set >>>反向结果维多必须加_set 
    # 这种方法也不行 查不了 所学知识没办法查啊

class Book(models.Model):
    title = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=8, decimal_places=2)
    authors = models.ManyToManyField(to=‘Author‘, through=‘Book2Author‘, through_fields=(‘book‘, ‘author‘))


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


class Book2Author(models.Model):
    book = models.ForeignKey(to=‘Book‘)
    buthor = models.ForeignKey(to=‘Author‘)
    # 基于第一种没有办法拓展我们第三张表中的字段 纯自动固定只有我们的Book和Author 拓展性极差
    info = models.CharField(max_length=64)

    res = models.Book.objects.filter(pk=1).values(‘authors__name‘)
    print(res)  # <QuerySet [{‘authors__name‘: ‘koko‘}]>
    # 有时数据库的原因会将数据卡主 需要手动更新 不然查不到数据 

   # 正向查
    # book_obj = models.Book.objects.filter(pk=1).first()
    # print(book_obj.authors.all())  # <QuerySet [<Author: Author object>]>
    # 正向按字段 结果为多的.all() 即可
    
    
    # 反向查  作者为yyy的书籍名称
    res = models.Author.objects.filter(name=‘yyy‘).values(‘book__title‘)
    print(res)  # <QuerySet [{‘book__title‘: ‘海贼王‘}]>