DjangoORM聚合查询和分组查询实现详解-创新互联

models.py：

from django.db import models 
# 出版社
class Publisher(models.Model):
  id = models.AutoField(primary_key=True)
  name = models.CharField(max_length=64, null=False, unique=True)
 
  def __str__(self):
    return "".format(self.name) 
 
# 书籍
class Book(models.Model):
  id = models.AutoField(primary_key=True)
  title = models.CharField(max_length=64, null=False, unique=True)
  price = models.DecimalField(max_digits=5, decimal_places=2, default=00.00) # 最长位数为 5，小数位数为 2，默认值为 00.00
  publisher = models.ForeignKey(to="Publisher", null=True) # 把 null 设置为 True
 
  def __str__(self):
    return "".format(self.title)
 
# 作者
class Author(models.Model):
  id = models.AutoField(primary_key=True)
  name = models.CharField(max_length=16, null=False, unique=True)
  book = models.ManyToManyField(to="Book") # 多对多关联 Book 表，ORM 会自动生成第 3 张表
 
  def __str__(self):
    return "".format(self.name)