191028DjangoORM之多表操做

1、多表操做之一對多

• 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')  #外鍵關聯

    def __str__(self):
        return self.name

# 做者和書的關係是多對多的關係
class Author(models.Model):
    name = models.CharField(max_length=20)

# 書和出版社的表是一對多的關係
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

一、插入數據

• 方式一

Book.objects.create(name="Liunx運維手冊",price=99,pub_date="2018-08-08",publish_id=2)  #直接對外鍵_id賦值

• 方式二

publish_obj = Publish.objects.filter(name="人民出版社")[0]
Book.objects.create(name="Liunx運維手冊2版",price=199,pub_date="2019-08-08",publish=publish_obj)  #直接對外鍵賦值

二、查詢數據

• 方式一

# 查詢書籍是由哪一個出版社出版的，正向查詢
book_obj = Book.objects.get(name="python")
print(book_obj.name)
print(book_obj.pub_date)
print(book_obj.publish.name)  #一對多中必定是一個對象
print(book_obj.publish.city)
print(type(book_obj.publish))

# 查詢出版社出過哪些書籍，反向查詢
pub_obj = Publish.objects.get(name="人民出版社")
print(pub_obj.book_set.all().values("name","price"))  #多對一查到的是一個集合

• 方式二

# 查詢出版社出過哪些書
ret = Book.objects.filter(publish__name="人民出版社").values("name","price")
print(ret)
# 查詢書的出版社
ret = Publish.objects.filter(book__name="python").values("name")
print(ret)
ret = Book.objects.filter(name="python").values("publish__name")
print(ret)

2、多表操做之多對多（自動維護多對多關係表）

• 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')  #外鍵關聯
    authors = models.ManyToManyField("Author")  #建立表多對多的關係
    def __str__(self):
        return self.name

# 做者和書的關係是多對多的關係
class Author(models.Model):
    name = models.CharField(max_length=20)
    age = models.IntegerField(default=0)
    def __str__(self):
        return self.name


# 書和出版社的表是一對多的關係
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

一、數據查找

• 根據書id查找做者

# 經過對象的方式建立多對多的綁定關係
book_obj = Book.objects.get(id=3)
print(book_obj.authors.all())  #這裏拿到的authors是書對應做者的對象

• 根據做者id查找書名

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

• 使用雙下劃線進行關聯查詢

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

二、添加對應關係

book_obj = Book.objects.get(id=5)  #獲取書的對象
author_objs = Author.objects.get(id=3)  #獲取做者的對象
book_obj.authors.add(author_objs)  #將做者對象加入到書的對應做者對象中，若是author_objs是一個集合則須要book_obj.authors.add(*author_objs)這樣寫

三、刪除對應關係

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

3、多表操做之多對多（手動維護多對多關係表）

• 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')  #外鍵關聯
    # authors = models.ManyToManyField("Author")  #建立表多對多的關係
    def __str__(self):
        return self.name

# 做者和書的關係是多對多的關係
class Author(models.Model):
    name = models.CharField(max_length=20)
    age = models.IntegerField(default=0)
    def __str__(self):
        return self.name

# 建立做者和書的關係綁定表
class Book_Author(models.Model):
    book = models.ForeignKey("Book",on_delete="CASCADE")
    author = models.ForeignKey("Author",on_delete="CASCADE")


# 書和出版社的表是一對多的關係
class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)

• 添加/查詢關係

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

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

• 查詢做者的書籍

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

4、聚合和分組查詢

• 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")))

• 分組

print(Book.objects.values("authors__name").annotate(Sum("price")))  #按照author_name分組後將price作求和
    print(Publish.objects.values("name").annotate(Min("book__price")))

• F函數

from django.db.models import Avg,Min,Sum,Max,Count,F
    Book.objects.all().update(price=F("price")*2)  #將書的價格翻一倍

• Q函數

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