models.py

from django.db import models

## Create your models here.


class Publisher(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32, unique=True)

    def __str__(self):
        return "Object:{}".format(self.name)


class Book(models.Model):
    id = models.AutoField(primary_key=True)
    price = models.DecimalField(max_digits=5, decimal_places=2, default=99.99)
    ## 库存数
    kucun = models.IntegerField(default=1000)
    ## 卖出数
    maichu = models.IntegerField(default=0)

    title = models.CharField(max_length=32)
    ## 外键
    ## related_name="books" 反向查询是用来代替 book_set的
    publisher = models.ForeignKey(
        to="Publisher",
        on_delete=models.CASCADE,
        related_name="books",
        related_query_name="xxoo",
        null=True
    )

    def __str__(self):
        return self.title


class Author(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    books = models.ManyToManyField(to="Book")

    def __str__(self):
        return self.name


class FixedCharField(models.Field):
    """
    自定义的char类型的字段类
    """
    def __init__(self, max_length, *args, **kwargs):
        self.max_length = max_length
        super(FixedCharField, self).__init__(max_length=max_length, *args, **kwargs)

    def db_type(self, connection):
        """
        限定生成数据库表的字段类型为char，长度为max_length指定的值
        """
        return 'char(%s)' % self.max_length


class Person(models.Model):
    name = models.CharField(max_length=32)
    age = models.IntegerField(default=18)
    birthday = models.DateField(auto_now_add=True)

    def __str__(self):
        return "<Person Object:{}>".format(self.name)

    ## class Meta:
    ##     ordering = ("birthday",)

例子：

##!/usr/bin/python3
## -*- coding: utf-8 -*-
## @Time    : 2019/6/26 16:49
## @Author  : Joker Bai
## @Email   : unclejoker520@163.com
## @File    : orm_test.py
## @Software: PyCharm
## @Function:
## @Version :
import  os
if __name__ == '__main__':
    ## 加载Django项目的配置信息
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "orm_test.settings")
    ## 导入Django，并启动Django项目
    import django
    django.setup()

    from orm import models

    ## 查询所有的人
    ret = models.Person.objects.all()
    print(ret)

    ## get查询，返回的是<class 'orm.models.Person'>
    ret = models.Person.objects.get(id=1)
    print(ret,type(ret))

    ## filter查询，返回的是<class 'django.db.models.query.QuerySet'>
    ret = models.Person.objects.filter(id=1)
    print(ret,type(ret))

    ## exclude
    ret = models.Person.objects.exclude(id=1)
    print(ret)

    ## values，返回的是QuerySet对象，里面都是字典，不写的话默认查出所有
    ret = models.Person.objects.values()
    print(ret)

    ## value_list，返回的是QuerySet对象，里面都是元组，不写的话默认返回所有
    ret = models.Person.objects.values_list()
    print(ret)

    ## order_by，安装指定的顺序排序
    ret = models.Person.objects.order_by("name")
    print(ret)

    ## reverse，将一个有序的的QuerySet进行反转
    ret = models.Person.objects.order_by("name").reverse()
    print(ret)

    ## count，返回QuerySet的数量
    ret = models.Person.objects.all().count()
    print(ret)

    ret = models.Publisher.objects.all().count()
    print(ret)

    ## first, 返回QuerySet中第一个对象
    ret = models.Publisher.objects.all().first()
    print(ret)

    ret = models.Publisher.objects.first()
    print(ret, type(ret))

    ## last，返回QuerySet中最后一个对象
    ret = models.Publisher.objects.all().last()
    print(ret, type(ret))

    print("单表查询之双下划线".center(80, "*"))
    ## 查询id值大于1小于4的结果
    ret = models.Publisher.objects.filter(id__gt=1, id__lt=4)
    print(ret)

    ## in，查询id在[1,3,5]中的结果
    ret = models.Publisher.objects.filter(id__in=[1,3,5, 10])
    print(ret)

    ## containers 字段包含
    ret = models.Book.objects.filter(title__contains="python")
    print(ret)

    ## icontainers 忽略大小写
    ret = models.Book.objects.filter(title__icontains="PYTHON")
    print(ret)

    ## range 在什么范围之内，相当于between...and...
    ret = models.Book.objects.filter(id__range=[3, 7])
    print(ret)

    print("外键查询".center(80, "*"))
    ## 正向查询
    book_obj = models.Book.objects.first()
    print(book_obj, type(book_obj))
    print(book_obj.publisher.name)

    ## 查询ID=3的书的出版社的名称，双下划线跨表查询
    print(models.Book.objects.filter(id=3))
    ret = models.Book.objects.filter(id=3).values_list("publisher__name")
    print(ret)

    ## 反向查询
    ## 1、基于对象查询
    publisher_obj = models.Publisher.objects.get(id=1)
    ret = publisher_obj.books.all()
    print(ret)

    ## 2、基于双下划线，查询出版社id=1的所有书籍
    ret = models.Publisher.objects.filter(id=1).values_list("xxoo__title")
    print(ret)

    print("多对多查询".center(80, "*"))
    ## 查询
    author_obj = models.Author.objects.get(id=1)
    print(author_obj)

    ## 查询Alex写过的书
    ret = author_obj.books.all()
    print(ret)

    ## create 通过作者创建一本书
    ## author_obj.books.create(title="全民出击", publisher_id=1)

    ## add 添加一本书id=7的书
    ## book_obj = models.Book.objects.get(id=7)
    ## author_obj.books.add(book_obj)

    ## 添加多个书籍
    ## book_obj = models.Book.objects.filter(id__gt=6)
    ## print(book_obj)
    ## author_obj.books.add(*book_obj)

    ## 直接添加id
    ## author_obj.books.add(9)

    ## remove 把alex的全民出击删掉
    ## book_obj = models.Book.objects.filter(title="全民出击")
    ## print(book_obj)
    ## author_obj.books.remove(*book_obj)

    ## 删除id=7的书籍
    ## author_obj.books.remove(7)

    ## clear 把jack的书都清掉
    ## jack_obj = models.Author.objects.get(name="jack")
    ## jack_obj.books.clear()

    ## 外键的反向操作
    ## 找到id=1的出版社
    ## publisher_obj = models.Publisher.objects.get(id=1)
    ## publisher_obj.books.clear()

    print("聚合操作".center(80, "*"))
    from django.db.models import Avg, Sum, Max, Min, Count
    ## 计算所有书籍的平均值
    ret = models.Book.objects.all().aggregate(price_avg = Avg("price"))
    print(ret)

    ## 查找所有书籍中价格最高、最低、总和
    ret = models.Book.objects.all().aggregate(price_max = Max("price"), price_min =Min("price"), price_sum=Sum("price"))
    print(ret)

    print("分组查询".center(80, "*"))
    ## 查询每一本书的作者个数
    ret = models.Book.objects.all().annotate(author_num = Count("author"))
    print(ret)
    for book in ret:
        print("书名：{}  >>>>>>  作者个数：{}".format(book.title, book.author_num))

    ## 查询作者数量大于0的书
    ret = models.Book.objects.all().annotate(author_num = Count("author")).filter(author_num__gt=0)
    print(ret)
    for book in ret:
        print("书名：{}  >>>>>>  作者个数：{}".format(book.title, book.author_num))

    ## 查询每个作者出的书的总价格
    ret = models.Author.objects.all().annotate(price_sum = Sum("books__price"))
    print(ret)
    for author in ret:
        print("作者：{} >>>>>> 总价格：{}".format(author, author.price_sum))

    print("F和Q查询".center(80, "*"))
    from django.db.models import F,  Value, Q
    from django.db.models.functions import Concat
    ## 查询库存数大于卖出书的所有书
    ret = models.Book.objects.filter(kucun__gt=F("maichu"))
    print(ret)

    ## 把每一本的卖出数都乘3
    ## models.Book.objects.update(maichu=(F("maichu")+1)*3)

    ## 把每一本书的书名后面加上“第一版”
    ## models.Book.objects.update(title=Concat(F("title"), Value("第一版")))

    ## 查询卖出数大于1000，价格小于100的书
    ret = models.Book.objects.filter(maichu__gt=1000, price__lt=100)
    print(ret)

    ## 查询卖出数大于1000，或者价格小于100的书
    ret = models.Book.objects.filter(Q(maichu__gt=1000) | Q(price__lt=100))
    print(ret)

    ## Q查询和字段查询同时存在时， 字段查询要放在Q查询的后面
    ret = models.Book.objects.filter(Q(maichu__gt=1000) | Q(price__lt=100), title__contains="python")
    print(ret)