select_related()的作用

select_related()是Django ORM（对象关系映射）中的一种查询优化方法，主要用于减少数据库查询次数，提高查询效率。当你在查询一个模型实例时，如果这个实例有ForeignKey关联到其他模型，那么select_related()可以帮助你在一次数据库查询中同时获取到这些关联模型的数据。

1，创建应用

Test/app12

python manage.py startapp app12

2，注册应用

Test/Test/settings.py

3，添加应用路由

Test/Test/urls.py

from django.contrib import admin from django.urls import path, include  urlpatterns = [     path('app12/', include('app12.urls')), ]

4，添加模型

Test/app12/models.py

# models.py from django.db import models  class Author(models.Model):     name = models.CharField(max_length=100)      def __str__(self):         return self.name  class Post(models.Model):     title = models.CharField(max_length=200)     content = models.TextField()     author = models.ForeignKey(Author, on_delete=models.CASCADE)      def __str__(self):         return self.title

5，添加视图函数

Test/app12/views.py

# views.py from django.shortcuts import render from .models import Post  def post_list(request):     posts = Post.objects.select_related('author').all()     return render(request, '12/post_list.html', {'posts': posts})

6，添加html代码

Test/templates/12/post_list.html

 {% for post in posts %}     
{{ post.title }}
     
By: {{ post.author.name }}
     
{{ post.content }}
 {% endfor %}

7，添加路由地址

from django.urls import path from . import views  urlpatterns = [      path('post_list/', views.post_list, name='post_list'), ]

8，添加数据

Test/add_data.py

import os import django import random from faker import Faker  os.environ.setdefault("DJANGO_SETTINGS_MODULE", "Test.settings") django.setup()  from app12.models import Author, Post  fake = Faker()  def add_data():     for _ in range(100):         author = Author.objects.create(name=fake.name())         for _ in range(10):             Post.objects.create(                 title=fake.sentence(),                 content=fake.text(),                 author=author             )  if __name__ == '__main__':     add_data()

9，访问页面

127.0.0.1:8000/app12/post_list/