Django select_related()方法

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

<!-- post_list.html -->
{% for post in posts %}
    <h2>{{ post.title }}</h2>
    <p>By: {{ post.author.name }}</p>
    <p>{{ post.content }}</p>
{% 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()