191028DjangoORM之多表操作

一、多表操作之一对多

• models.py

from django.db import models

class Book(models.Model):
    name = models.CharField(max_length=30)
    price = models.FloatField()
    pub_date = models.DateField()
    publish = models.ForeignKey('Publish',on_delete='CASCADE')  #外键关联

    def __str__(self):
        return self.name

# 作者和书的关系是多对多的关系
class Author(models.Model):
    name = models.CharField(max_length=20)

# 书和出版社的表是一对多的关系
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

1、插入数据

• 方式一

Book.objects.create(name="Liunx运维手册",price=99,pub_date="2018-08-08",publish_id=2)  #直接对外键_id赋值

• 方式二

publish_obj = Publish.objects.filter(name="人民出版社")[0]
Book.objects.create(name="Liunx运维手册2版",price=199,pub_date="2019-08-08",publish=publish_obj)  #直接对外键赋值

2、查询数据

• 方式一

# 查询书籍是由哪个出版社出版的，正向查询
book_obj = Book.objects.get(name="python")
print(book_obj.name)
print(book_obj.pub_date)
print(book_obj.publish.name)  #一对多中一定是一个对象
print(book_obj.publish.city)
print(type(book_obj.publish))

# 查询出版社出过哪些书籍，反向查询
pub_obj = Publish.objects.get(name="人民出版社")
print(pub_obj.book_set.all().values("name","price"))  #多对一查到的是一个集合

• 方式二

# 查询出版社出过哪些书
ret = Book.objects.filter(publish__name="人民出版社").values("name","price")
print(ret)
# 查询书的出版社
ret = Publish.objects.filter(book__name="python").values("name")
print(ret)
ret = Book.objects.filter(name="python").values("publish__name")
print(ret)

二、多表操作之多对多（自动维护多对多关系表）

• models.py

from django.db import models

# Create your models here.

class Book(models.Model):
    name = models.CharField(max_length=30)
    price = models.FloatField()
    pub_date = models.DateField()
    publish = models.ForeignKey('Publish',on_delete='CASCADE')  #外键关联
    authors = models.ManyToManyField("Author")  #创建表多对多的关系
    def __str__(self):
        return self.name

# 作者和书的关系是多对多的关系
class Author(models.Model):
    name = models.CharField(max_length=20)
    age = models.IntegerField(default=0)
    def __str__(self):
        return self.name

# 书和出版社的表是一对多的关系
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

1、数据查找

• 根据书id查找作者

# 通过对象的方式创建多对多的绑定关系
book_obj = Book.objects.get(id=3)
print(book_obj.authors.all())  #这里拿到的authors是书对应作者的对象

• 根据作者id查找书名

author_obj = Author.objects.get(id=2)
print(author_obj.book_set.all())

• 使用双下划线进行关联查询

ret = Book.objects.filter(authors__name="maria").values("name","price")
print(ret)

2、添加对应关系

book_obj = Book.objects.get(id=5)  #获取书的对象
author_objs = Author.objects.get(id=3)  #获取作者的对象
book_obj.authors.add(author_objs)  #将作者对象加入到书的对应作者对象中，如果author_objs是一个集合则需要book_obj.authors.add(*author_objs)这样写

3、删除对应关系

book_obj = Book.objects.get(id=5)
author_objs = Author.objects.get(id=3)
book_obj.authors.remove(author_objs)

三、多表操作之多对多（手动维护多对多关系表）

• models.py

from django.db import models

# Create your models here.

class Book(models.Model):
    name = models.CharField(max_length=30)
    price = models.FloatField()
    pub_date = models.DateField()
    publish = models.ForeignKey('Publish',on_delete='CASCADE')  #外键关联
    # authors = models.ManyToManyField("Author")  #创建表多对多的关系
    def __str__(self):
        return self.name

# 作者和书的关系是多对多的关系
class Author(models.Model):
    name = models.CharField(max_length=20)
    age = models.IntegerField(default=0)
    def __str__(self):
        return self.name

# 创建作者和书的关系绑定表
class Book_Author(models.Model):
    book = models.ForeignKey("Book",on_delete="CASCADE")
    author = models.ForeignKey("Author",on_delete="CASCADE")

# 书和出版社的表是一对多的关系
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

• 添加/查询关系

    Book_Author.objects.create(book_id=1,author_id=2)

    obj = Book.objects.get(id=1)
    print(obj.book_author_set.all()[0].author)

• 查询作者的书籍

    ret = Book.objects.filter(book_author__author__name='maria').values("name","price")
    print(ret)

四、聚合和分组查询

• 聚合

from django.db.models import Avg,Min,Sum,Max,Count
    print(Book.objects.all().aggregate(Avg("price")))  #求平均值
    print(Book.objects.all().aggregate(Sum("price")))  #求和
    print(Book.objects.filter(authors__name="maria").aggregate(Sum("price")))  #求和
    print(Book.objects.filter(authors__name="maria").aggregate(Count("name")))

• 分组

    print(Book.objects.values("authors__name").annotate(Sum("price")))  #按照author_name分组后将price做求和
    print(Publish.objects.values("name").annotate(Min("book__price")))

• F函数

from django.db.models import Avg,Min,Sum,Max,Count,F
    Book.objects.all().update(price=F("price")*2)  #将书的价格翻一倍

• Q函数

from django.db.models import Avg,Min,Sum,Max,Count,F,Q
    print(Book.objects.filter(Q(price=178)|Q(name="python")))  #或
    print(Book.objects.filter(Q(price=178)| ~Q(name="python")))  #或非