Django学习笔记之数据库（一）

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安装

首先就是安装Mysql和Navicat。

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一、数据库配置

其实整个就是连接前端和连后端，因此需要做后端配置，
首先在整体的setting.py 中找到DATABASES，然后修改到自己的配置

DATABASES = {'default': {'ENGINE': 'django.db.backends.mysql','NAME':  'database_demo','USER': 'root','PASSWORD': 'admin','HOST': '127.0.0.1','PORT': '3306',}

然后添加自己的APP

INSTALLED_APPS = ['django.contrib.admin','django.contrib.auth','django.contrib.contenttypes','django.contrib.sessions','django.contrib.messages','django.contrib.staticfiles','home','databasesdemo'
]

在urls.py中添加自己的App的Url的分段地址，这里是 path(‘databases/’,include(“databasesdemo.urls”)),前面是上一篇连接前端的

 # 分段地址path('movie/',include("movie.urls")),#########################path('home/',include("home.urls")),#########################path('databases/',include("databasesdemo.urls")),

在APP下的model.py写数据表所需的字段和需求

from django.db import models
class BookModel(models.Model):name = models.CharField(max_length=100)author = models.CharField(max_length=20)pub_time = models.DateTimeField(auto_now_add=True)price = models.FloatField(default=0)

在pycharm 终端中做迁移操作

python manage.py makemigrations

执行完这个后会出现

0001_initial.py这个文件
还是在终端做python manage.py migrate映射操作，从而迁移到数据库中

python manage.py migrate

二、基本操作步骤

1.增加

在所在App下的view.py中增加代码

def add_book(request):#books=BookModel(name='三国演义',author='罗贯中',price=100)books = BookModel(name='水浒传', author='施耐庵', price=99)books.save()return HttpResponse('图书插入成功')

urls.py连接一下前端路径

from django.urls import path
from . import views
#指定应用名称
app_name="databasesdemo"
urlpatterns = [path("databasebookadd/",views.add_book,name="databasebookadd"),]

2.查看

在所在App下的view.py中查看代码

def query_book(request):#books=BookModel.objects.all()#books=BookModel.objects.filter(name='三国演义')#for book in books:#    print(book.id,book.name,book.author,book.pub_time,book.price)try:books = BookModel.objects.get(name='三国演义1')print(books.name)except BookModel.DoesNotExist:print("图书不存在")return HttpResponse('查找成功')

其中objects.filter和objects…all返回一个数组，因此，修改时候用get，删除时候用filter
urls.py连接一下前端路径

path("databasebookquery/",views.query_book,name="databasebookquery"),

3.排序

在所在App下的view.py中查看代码

def order_book(request):books=BookModel.objects.order_by("-pub_time")for book in books:print(book.id,book.name,book.author,book.pub_time,book.price)return HttpResponse('排序成功')

order_by(“pub_time”)为从小往大正序，order_by(“-pub_time”)为从大往小的倒序，只多一个负号就行

urls.py连接一下前端路径

 path("databasebookorder/",views.order_book,name="databasebookorder"),

4.更新

在所在App下的view.py中查看代码

def update_book(request):oldbook=BookModel.objects.get(name='三国演义')oldbook.name='西游记'oldbook.save()return  HttpResponse('修改成功')

这里就是get找到，然后替换

urls.py连接一下前端路径

path("databasebookupdate/",views.update_book,name="databasebookupdate"),

5.删除数据

代码如下（示例）：

def delete_book(request):book=BookModel.objects.filter(name='西游记')book.delete()return  HttpResponse('删除成功')

urls.py连接一下前端路径

path("databasebookdelete/", views.delete_book, name="databasebookdelete"),

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三、一对多，多对多，一对一

1.一对多

在model.py中定义两个表其中 Article中author，是User的外键

from django.db import modelsclass User(models.Model):username = models.CharField(max_length=20)password = models.CharField(max_length=100)class Article(models.Model):title = models.CharField(max_length=100)content = models.TextField()author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='articles'

在view中定义关系

from django.shortcuts import render, HttpResponse
from django.db import connection
from datetime import datetime
from .models import User,Article
# Create your views here.
def article_test(request):user = User(username='张三',password='111111')user.save()# user = User.objects.first()article = Article(title='ChatGPT6',content='okk',author=user)article.save()return HttpResponse("添加成功")# article=Article.objects.first()# return HttpResponse(article.author.username)
def one_to_many(request):user = User.objects.first()#articles = user.articles.all()  # 使用 related_name='articles'articles = user.articles.filter(title__contains="Chat").all()for article in articles:print(article.title)return HttpResponse("一对多查询成功")

这里可以看到author_id是连接的外键

最后url.py

from django.urls import path
from . import views
#指定应用名称
app_name="article"
urlpatterns = [path("articletest",views.article_test,name="article_test"),path("one_to_many",views.one_to_many,name="one_to_many"),
]

1.一对一

class UserExtension(models.Model):birthday = models.DateTimeField(null=True)school=models.CharField(blank=True,max_length=50)user = models.OneToOneField('User', on_delete=models.CASCADE)

1.多对多

class Article(models.Model):title = models.CharField(max_length=100)content = models.TextField()author = models.ForeignKey('User', on_delete=models.CASCADE, related_name='articles')tags = models.ManyToManyField('Tag',related_name='articles')

class Tag(models.Model):name = models.CharField(max_length=100)

四、查询操作

__exact精确查找
__iexact忽略大小写
__contains包含查找
__icontains忽略大小写 包含查找
__in 容器为list迭代查找
__range 范围

def query1(request):# __exact精确查找#article=Article.objects.filter(id__exact=1)# __iexact忽略大小写#article=Article.objects.filter(title__iexact='chatgpt5')# __contains包含查找#article=Article.objects.filter(title__contains='GPT')# __icontains忽略大小写 包含查找article = Article.objects.filter(title__icontains='gpt')# __in 容器为list迭代查找#article = Article.objects.filter(id__in=[1,2,3])#__range 范围start_date = datetime(year=2024,month=12,day=20)end_date = datetime(year=2025, month=1, day=8)article = Article.objects.filter(pub_time__range=(start_date,end_date))# 查看执行的语句可以用queryprint(article.query)print(article)for index in article:print(index.title)return HttpResponse('查找成功T')def query2(request):# 查找标题中，包含chat的文章的用户usr=User.objects.filter(articles__title__icontains='chat')for index in usr:print(index.id)print(usr.query)print(usr)return HttpResponse('查找成功T')

五、聚合操作

求平均值
result=Book.objects.aggregate(book_avg = Avg(‘price’))
求个数总和
result = Book.objects.aggregate(book_count = Count(‘id’))
求最大值最小值
result = Author.objects.aggregate(author_max=Max(‘age’),author_min=Min(‘age’))
都是.aggregate都在一个表里面折腾

from django.shortcuts import render
from django.db.models import Avg, Count, Max, Min, Sum
from django.shortcuts import render, HttpResponse
from .models import Book,BookOrder,Publisher,Author
# Create your views here.
def aggregate_view(request):#求平均值# result=Book.objects.aggregate(book_avg = Avg('price'))# 求个数总和# result = Book.objects.aggregate(book_count = Count('id'))# 求最大值最小值result = Author.objects.aggregate(author_max=Max('age'),author_min=Min('age'))print(result)return HttpResponse('MaxMin_view')

annotate会使用当前这个模型的主键进行分组，bookorder 是模型 BookOrder 的简称，Sum(“bookorder__price”) 会计算每个 Book 对象的所有相关 BookOrder 对象的 price 字段的总和。

def annotate_view(request):# 求分组总和result = Book.objects.annotate(total=Sum("bookorder__price")).values('name','total')print(result)return HttpResponse('Sum_view')

六、F和Q操作

filter 方法的条件语句需要使用 Q 对象来表示复杂查询（如逻辑或 OR 操作）。直接在 filter 中使用 Python 的 or 关键字是无效的，因为它不会被 Django 解析为 SQL 查询。

def q_view(request):books=Book.objects.filter(Q(price__gte=86)|Q(rating__gte=9)).all()for book in books:print(book.name,book.price,book.rating)return HttpResponse('q_view')

使用 F 对象和 update 方法可以直接在数据库层面进行批量更新，避免了将大量对象加载到内存中进行修改的性能开销。

def f_view(request):Book.objects.update(price=F('price')-10)return HttpResponse('f_view')