[django]django的orm查询

实体	实体
出版社	category
作者	tag
书	文章

先学习一下基础的增删查改

django orm增删改查: https://www.cnblogs.com/iiiiiher/articles/8870906.html

## 增加
- 方法1:
People.objects.create(usernmae='maotai',age=22);

- 方法2:
p = People()
p.name = "maomao"
p.age = 23
p.save()


## 更新

## 查询: crud,重点是查询
- 查询所有列
People.objects.all()
[obj,obj2]

- 查询某几列
People.objects.all().values("id","username")
[{name:maotai,age:22},{name:maomao,age:22}]

People.objects.all().values_list("id","username")
[(1, 'maotai'), (2, 'maomai')]


People.objects.all()
<QuerySet [<People: name: maotai, age: 22>, <People: name: maomai, age: 23>, <People: name: maodou, age: 24>]>
People.objects.all().values('id','username')
<QuerySet [{'id': 1, 'username': 'maotai'}, {'id': 2, 'username': 'maomai'}, {'id': 3, 'username': 'maodou'}]>
People.objects.all().values_list('id','username')
<QuerySet [(1, 'maotai'), (2, 'maomai'), (3, 'maodou')]>


## 命令行查看真实sql
print(People.objects.all().query)

from django.shortcuts import render,HttpResponse

# Create your views here.
from app01.models import *

def index(request):

    return render(request,"index.html")

def addbook(request):

    # b=Book(name="python基础",price=99,author="mao",pub_date="2017-12-12")
    # b.save()
    Book.objects.create(name="linux",price=78,author="maotai",pub_date="2016-12-12")
    #Book.objects.create(**dic)

    return HttpResponse("添加成功")


def update(request):

    Book.objects.filter(author="mao").update(price=999)

    # b=Book.objects.get(author="maotai")
    # b.price=120
    # b.save()
    # print(b)#<QuerySet [<Book: Book object>]>
    # print(type(b))

    return HttpResponse("修改成功！")


def delete(req):

    Book.objects.filter(author="maotai").delete()

    return HttpResponse("success")

def select(req):
    # book_list=Book.objects.all()
    # print(book_list)
    # print(book_list[0])#Book object
    # book_list = Book.objects.filter(id=2)
    # book_list = Book.objects.all()[::2]
    # book_list = Book.objects.all()[::-1]
    # book_list = Book.objects.first()
    # book_list = Book.objects.last()
    # book_list = Book.objects.get(id=2)#只能取出一条记录时才不报错
    # ret1=Book.objects.filter(author="maotai").values("name")
    # ret2=Book.objects.filter(author="mao").values_list("name","price")
    # book_list=Book.objects.exclude(author="mao").values("name","price")
    # print(ret1)
    # print(ret2)

    # book_list= Book.objects.all().values("name").distinct()
    # book_count= Book.objects.all().values("name").distinct().count()
    # print(book_count)

    #万能的  __

    # book_list=Book.objects.filter(price__gt=50).values("name","price")
    book_list=Book.objects.filter(name__contains="P").values_list("name","price")


    return render(req,"index.html",{"book_list":book_list})

终极吐血整理版--2018年4月23日 17:56:27

实体	实体
出版社	category
作者	tag
书	文章

一对多
    创建
        2种方法
    查询
        1,python这本书对应的出版社的名字
        2,邮电出版社出版的所有书
多对多
    创建(目的创建book和author关联关系)
        book_obj.publish # 这本书对应的出版社,对象
        book_obj.author  # 这个书的作者集合, querysetset
    
        book_obj.objects.all()
        book_obj.objects.add(*author_obj)
    查询
        1,通author找出他的book: 龟叔写的书找出来
        2,python这本书的作者
        
-
1, 一对多: 
    1, python这本书对应的出版社的名字
        Book.objects.filter(name="python").values('publish__name')
        Publish.objects.filter(book__name="python").values('name')


    2, 邮电出版社出版的所有书
        print(Publish.objects.filter(name="邮电出版社").values('book__name'))
        print(Book.objects.filter(publish__name="邮电出版社").values('name'))

-

2, 多对多查询
    1,通author找出他的book: 龟叔写的书找出来
        print(Book.objects.filter(author__name="龟叔"))
        print(Author.objects.filter(name="龟叔").values('book__name'))

    2,python这本书的作者
        print(Book.objects.filter(name="python").values('author__name'))
        print(Author.objects.filter(book__name="python").values('name'))

聚合查询和分组查询

聚合:

from django.db.models import Avg, Max, Min, Sum, Count
-
    print(Book.objects.aggregate(Min('price')))
    print(Book.objects.aggregate(Sum('price')))
    print(Book.objects.aggregate(Avg('price')))

    龟叔出的书的价格总和
        print(Book.objects.filter(author__name="龟叔").aggregate(Sum('price')))
        print(Book.objects.filter(author__name="龟叔").aggregate(guishu_money = Sum('price')))
-
    龟叔出了几本书?
        print(Book.objects.filter(author__name="龟叔").aggregate(Count('name')))

-
分组聚合:  
    每个作者的出的书的价格和.
        print(Book.objects.all().values("author__name").annotate(Sum("price")))
        print(Book.objects.values("author__name").annotate(Sum("price"))) #Book.objects.values分组,聚合
        
        # <QuerySet [{'author__name': None, 'price__sum': 108}, {'author__name': '林纳斯', 'price__sum': 89}, {'author__name': '毛台', 'price__sum': 89}, {'author__name': '龟叔', 'price__sum': 188}]>
-

        SELECT
            "app03_author"."name",
            SUM("app03_book"."price") AS "price__sum"
        FROM
            "app03_book"
        LEFT OUTER JOIN "app03_book_author" ON (
            "app03_book"."id" = "app03_book_author"."book_id"
        )
        LEFT OUTER JOIN "app03_author" ON (
            "app03_book_author"."author_id" = "app03_author"."id"
        )
        GROUP BY
            "app03_author"."name"
        LIMIT 21;

    查各个出版社出版的最便宜的书的价格(分组和聚合不一定用在复合查询)
        print(Publish.objects.values('name').annotate(Min("book__price")))
        print(Publish.objects.values('name').annotateabc=Min("book__price")))

F查询和Q查询

- F/Q 且,或,非关系查询

from django.db.models import F,Q


    1, 逗号: 且的关系
        print(Book.objects.get(name="python", price=77))

    2, F查询: 每本书price+10
        # Book.objects.all().update(price=price+10) #这种是错误的
        Book.objects.all().update(price=F('price') + 10)
    
    3, Q查询: 或的关系
        print(Book.objects.filter(Q(name='go') | Q(price=109)).values('name', 'price'))
    4, ~: 非的关系
        print(Book.objects.filter(Q(name='go') | ~Q(price=109)).values('name', 'price'))
    5,__contains: 包含关系
        print(Book.objects.filter(Q(name__contains='go')).values('name', 'price'))

queryset的特性([缓存]惰性机制)

queryset缓存:

1,只有调用结果时,才会执行sql
    res = Book.objects.all() # 可以理解为一堆sql
    print(res)               # 此时才会执行sql

2,queryset具备缓存特性,
    res = Book.objects.all() 
    for i in res: #第一次去执行sql,得到结果缓存
        print(i)
        
    print("*"*100)#第二次直接从缓存中取出数据
    for i in res:
        print(i)
        
3,缓存带来的危害, 中途遇到更新时,无法获取到最新值.
    res = Book.objects.all()
    for i in res:
        print(i.price) # 打印原价

    Book.objects.all().update(price=200)

    for i in res:
        print(i.price) # 更新原价
4,加入只想判断结果res.exists()

    res = Book.objects.filter(price=100)
    if res.exists(): #不会将一坨数据扔进缓存
        print('ok')

5.如果结果非常巨大(返回迭代器)
    objs = Book.objects.all().iterator()
注: 迭代器只允许迭代一次.

可迭代
    # print(objs[1])
    # print(objs[1:4])
    # print(objs[::-1])
可切片
-

models操作

参考

思路:

给publish插数据
给book插数据
给author插数据

给book_author插数据
    调用外键:     Book.publish # 这本书对应出版社的一条记录(对象)
    调用多对多键: Book.author  # 这本书绑定关系的作者的记录(queryset)
    book_obj.author.all()
    book_obj.author.add(author_obj)
    book_obj.author.remove(author_obj)

    author_obj = Author.objects.all()
    book_obj.author.add(*author_obj)
    
通过book找它的author: 
    python这本书的作者
        Author.objects.filter(book__name="python")

通过author找它的book
    龟叔出过的书的name+price(用系统自带的manytomany方法)
        Book.objects.filter(author__name="龟叔").values('name', 'price')


自定义book_author表:
    查出id=2的book的author:(两张表借助第三张表book_author取数据)
    
    方法1:
        book_obj = Book.objects.get(id=2)
        book_obj.book_author_set.all() # book_author的queryset对象
        print(book_obj.book_author_set.all()[0].author) # 查出作者.
    方法2:
        Book.objects.filter(book_author__author_id__name="龟叔").values('name','price')

多对多:
    创建多对多关系:
        author = models.ManytoManyFiled("Author")
        
    book对象它的所有的关联作者: obj = book_obj.authors.all()
        绑定多对多的关系:       obj.add(*QuerySet)
                                obj.add(author_obj)
        如果想向第三张表插入值的方式绑定:
            手动创建第三张表
                class Book_Author(models.Model):
                    book_id = models.ForeignKey(Book, on_delete=models.CASCADE)
                    author_id = models.ForeignKey(Author, on_delete=models.CASCADE)
                Book_Author.objects.create(book_id=2,author_id=3)
    掌握: 通过filter value(双下划线)实现多对多的关联查询
        龟叔出过的书的name+price(用系统自带的manytomany方法)
            Book.objects.filter(author__name="龟叔").values('name', 'price')

1.聚合
2.分组
3.F查询和Q查询

多表查询:
    一对多
        1,sql
        2,set
        3,__
            图书---2种-->出版社
            图书<--1种--出版社

    多对多
        1,自动
            操作第三张表, 为第三张表添加记录.
            调用外键:     Book.publish # 这本书对应出版社的一条记录(对象)
            
            调用多对多键: Book.author  # 这本书绑定关系的作者的记录(对象)
        2,手动
        
        通过book找它的author
        通过author找它的book
        
        给book添加author记录
            即手动添加book_author关系
                1,取出一本书 book_obj
                2,取出一个作者author_obj
                3,book_obj.add(author_obj)

F查询和Q查询

1.创建
    1,p = People
      p.name = "mt"
      p.save()
    2,People.objects.create(name="mt")

2.查询(重点****)
    def home(request):
        book_list = Book.objects.filter(id=1)
        book_list = Book.objects.exclude(author='maotai').values('name', 'price')
        
        # filter/all 取出的是一个queryset
        book_list = Book.objects.all()
        book_list = Book.objects.all()[::2]
        book_list = Book.objects.all()[::-1]

        # first/last get取到的是一个实例
        book_list = Book.objects.first()
        book_list = Book.objects.last()
        book_list = Book.objects.get(id=1) # 结果超过一个后会报错

        res = Book.objects.filter(author='maotai').values("name")              # 结果是字典形式,kv
        res = Book.objects.filter(author='maotai').values_list("name","price") # 结果是列表形式,好像只有key
        # select name from book where author='maotai';

        book_list = Book.objects.filter(author='maotai').values("name").distinct() # filter某些字段时, 去重
        book_count = Book.objects.all().values("name").count()   # 记录条数
        
        # 模糊匹配
        book_list = Book.objects.filter(name__contains="mao").values_list("name","price")
        book_list = Book.objects.filter(id__gt=5).values_list('name','price')

3,删除
    book_list = Book.objects.exclude(author='maotai').delete()

- 方法小结:
all()&filter()
    queryset.update()
    queryset.delete()

first/last&get
    obj.save()

思路:
创建publish出版社/图书表(一对多)---添加图书的两种方法(主要是给publish_id赋值)
                                    1, 
                                        Book.objects.create(name="流畅的python", price=89, pub_date="2017-06-06", publish_id=3)
                                    2, 
                                        publish_obj = Publish.objects.filter(name="人民出版社")[0]
                                        Book.objects.create(name="go action", price=22, pub_date="2018-04-04", publish=publish_obj)
-
1. 通过book查publish消息?
    1,def __str__
    2,查询publish的其他字段
    
2. 查看人民出版社出版过哪些书?
    1,方法1: 正向
    2,方法2: 逆向查: 利用django自带的book_set
    
多表操作(一对多):
    1,正向查询
        pub_obj = Publish.objects.get(name="人民出版社")
        res = Book.objects.filter(publish=pub_obj).values('name', 'price')
    2,逆向查询,利用django提供的book_set
        pub_obj = Publish.objects.filter(name="人民出版社")[0]
        print(pub_obj.book_set.all())
        print(type(pub_obj.book_set.all()))

- 
外键两种写法:
    1,外键加引号
        publish = models.ForeignKey("publish", on_delete=models.CASCADE, verbose_name="出版社")
    2,外键不加引号.(外键model需要先定义)
        publish = models.ForeignKey(Publish, on_delete=models.CASCADE, verbose_name="出版社")




通过__方法查找结果:
    1,逆向查找: 外键__名称
    - 查出人民出版社出版的图书
    res = Book.objects.filter(publish__name="人民出版社").values('name', 'price') # 这里的publish是外键名
    print("3,通过__方法查找结果: ", res)
    print("-" * 50)

    2,正向查找: 主表__name
    2.1
    # python这本书的出版社名字
    print(Publish.objects.filter(book__name="python").values('name')) # 这里的book是表名, 这里name是publish表里的字段name
    return HttpResponse("查询完毕, 结果请查看console")

    2.2通过逆向查
    res = Book.objects.filter(name="python").values("publish__name") # select publish__name


栗子
思路: 一对多: 这个出版社出版过哪些书? -- 这本书是哪个出版社出版的?
      多对多: id=3的作者的信息

    1. 人民出版社出版的图书的名字
        1.1
        pub_obj = Publish.objects.get(name="人民出版社")
        res = Book.objects.filter(publish=pub_obj).values('name', 'price')
        
        1.2
        pub_obj = Publish.objects.filter(name="人民出版社")[0]
        print(pub_obj.book_set.all())
        
        1.3
        res = Book.objects.filter(publish__name="人民出版社").values('name', 'price')
    

    2. python这本书的出版社名字
        2.1逆向(主表名__)
        res = Publish.objects.filter(book__name="python").values('name')
    
        2.2正向(外键名__)
        res = Book.objects.filter(name="python").values("publish__name")

    3. 在北京出版社出版的书
    Book.objects.filter(publish__city__="北京").values('name')
    
    4. 2017年上半年出的书的出版社名字
    res = Book.objects.filter(pub_date__lt="2017-07-01", pub_date__gt="2017-01-01").values('publish_name')

    5, 多对多的关系, id=3的所有作者信息
    book_obj = Book.objects.get(id=3)
    book_obj.author.all()
    print(type(book_obj.author.all()))

数据模拟:

publish
author
book
    Foreign_key: publish
    ManyToMany:  author

核心点:
    一对多创建关系
    一对多查询

publish:
1   人民出版社   北京
2   邮电出版社   西安
3   机械出版社   上海


book:
id  name    price    pub_date     publish
1   python  89       2017-01-07       1
2   go      99       2017-04-01       2
3   java    39       2017-06-01       3
4   ios     69       2017-12.24       3



Author:
id  name    age
1   龟叔    17
2   林纳斯  20
3   毛台    25
1   Jeff    42


book_author:
id  book_id    author_id
1   1          1
2   1          2
3   2          3
4   2          3

- models

class Publish(models.Model):
    name = models.CharField(max_length=40, verbose_name="出版社")
    city = models.CharField(max_length=40, verbose_name="出版社所在城市")

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = "出版社"
        verbose_name_plural = verbose_name


class Author(models.Model):
    name = models.CharField(max_length=40, verbose_name="作者")
    age = models.IntegerField(default=17, verbose_name="年龄")

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = "作者"
        verbose_name_plural = verbose_name


class Book(models.Model):
    name = models.CharField(max_length=40, verbose_name="书名")
    price = models.IntegerField(default=99, verbose_name="价格")
    pub_date = models.DateField(verbose_name="出版时间")
    publish = models.ForeignKey(Publish, on_delete=models.CASCADE, verbose_name="出版社")

    # author = models.ManyToManyField(Author, verbose_name="作者")

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = "图书"
        verbose_name_plural = verbose_name


class Book_Author(models.Model):
    book_id = models.ForeignKey(Book, on_delete=models.CASCADE)
    author_id = models.ForeignKey(Author, on_delete=models.CASCADE)

- views

def addbook(request):
    # 1.创建出版社
    # Publish.objects.create(name="人民出版社",city="北京")
    #
    # p = Publish()
    # p.name = "邮电出版社"
    # p.city = "西安"
    # p.save()
    #
    # p2 = Publish(name="机械出版社")
    # p2.city = "上海"
    # p2.save()
    #
    # print(Publish.objects.all())

    # 2，创建图书
    # Book.objects.create(name="python", price=89,pub_date='2017-01-07', publish_id=1)
    # Book.objects.create(name="go", price=99, pub_date='2017-04-01',publish_id=2)
    # Book.objects.create(name="ios", price=39,pub_date='2017-06-01', publish_id=3)
    # Book.objects.create(name="java", price=69, pub_date='2017-12-24',publish_id=3)

    # 3，创建作者
    # Author.objects.create(name="龟叔",age=17)
    # Author.objects.create(name="林纳斯",age=20)
    # Author.objects.create(name="毛台",age=25)
    # Author.objects.create(name="Jeff",age=33)

    # 龟叔还写了ios
    # book_obj = Book.objects.get(name="ios")
    # author_obj = Author.objects.get(id=1)
    # print(book_obj.author.all()) # ios谁写的?
    # # book_obj.author.add(author_obj)

    # 龟叔出过的书
    # res = Book.objects.filter(author__name="龟叔").values('name', 'price')
    # print(res)
    #
    # # python这本书谁写的
    # res2 = Author.objects.filter(book__name="python")
    # print(res2)
    #
    Book_Author.objects.create(book_id=2,author_id=1)

    book_obj = Book.objects.get(id=2)
    # book_obj.book_author_set.all() # book_author的queryset对象
    print(book_obj.book_author_set.all()[0].author)

    Book.objects.filter(book_author__author_id__name="龟叔").values('name','price')


    # 创建自定义book_author表
    Book.objects.filter(book_author__author__name="alex").values("name","price")
    return HttpResponse("结果请查看console")

查看sql

追加扫settings.py

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'console':{
            'level':'DEBUG',
            'class':'logging.StreamHandler',
        },
    },
    'loggers': {
        'django.db.backends': {
            'handlers': ['console'],
            'propagate': True,
            'level':'DEBUG',
        },
    }
}