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prefetch_related()是 Django ORM 中用于优化查询性能的另一个重要方法,尤其在处理多对多(ManyToMany)关系和反向关系时非常有用。它允许你预加载相关对象,从而减少数据库查询次数。
Test/app13
python manage.py startapp app13
Test/Test/settings.py
- from django.contrib import admin
- from django.urls import path, include
-
- urlpatterns = [
-
- path('app13/', include('app13.urls')),
- ]
Test/app13/models.py
- from django.db import models
- class Author(models.Model):
- name = models.CharField(max_length=100)
- class Book(models.Model):
- title = models.CharField(max_length=100)
- authors = models.ManyToManyField(Author)
- class Review(models.Model):
- book = models.ForeignKey(Book, on_delete=models.CASCADE)
- rating = models.IntegerField()
Test/app13/views.py
- from django.shortcuts import render
- from .models import Book, Author, Review
-
- def book_list(request):
- # 使用 prefetch_related 预加载作者和评论信息
- books = Book.objects.prefetch_related('authors', 'review_set').all()
-
- # 准备传递给模板的上下文
- context = {
- 'books': books,
- }
-
- # 渲染并返回响应
- return render(request, '13/book_list.html', context)
Test/templates/13/book_list.html
- <!DOCTYPE html>
- <html lang="en">
- <head>
- <meta charset="UTF-8">
- <title>Title</title>
- </head>
- <body>
-
- {% for book in books %}
- <h2>{{ book.title }}</h2>
- <h3>Authors:</h3>
- <ul>
- {% for author in book.authors.all %}
- <li>{{ author.name }}</li>
- {% endfor %}
- </ul>
- <h3>Reviews:</h3>
- <ul>
- {% for review in book.review_set.all %}
- <li>Rating: {{ review.rating }}</li>
- {% endfor %}
- </ul>
- {% endfor %}
-
-
- </body>
- </html>
Test/app13/urls.py
- from django.urls import path
- from . import views
-
- urlpatterns = [
-
- path('book_list/', views.book_list, name='book_list'),
- ]
Test/populate_db.py
- import random
-
-
- import os
- import django
-
- os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'Test.settings')
- django.setup()
- from app13.models import Author, Book, Review
-
-
-
- # 创建随机作者
- for _ in range(10):
- author = Author(name=f'Author {_}')
- author.save()
-
- # 创建随机书籍
- for _ in range(20):
- book = Book(title=f'Book Title {_}')
- book.save()
- # 随机选择1-3个作者
- authors = Author.objects.all()
- book.authors.set(random.sample(list(authors), random.randint(1, 3)))
-
- # 创建随机评论
- for _ in range(50):
- review = Review(
- book=random.choice(Book.objects.all()),
- rating=random.randint(1, 5)
- )
- review.save()
-
http://127.0.0.1:8000/app13/book_list/
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