#Django性能优化 - 提升应用响应速度与并发能力

# ❌ 错误做法：遍历每篇文章时，单独查询作者、标签、评论
# posts = Post.objects.all()
# for post in posts:
#     print(post.author.username, [t.name for t in post.tags.all()])

# ✅ 正确做法：外键一对一用select_related，一对多多对多用prefetch_related
from django.db.models import Prefetch
from django.contrib.auth.models import User

class Tag(models.Model): name = models.CharField(max_length=50)
class Comment(models.Model): post = models.ForeignKey('Post', on_delete=models.CASCADE)
class Post(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    tags = models.ManyToManyField(Tag)
    comments = models.ManyToManyField(Comment)

posts = Post.objects.select_related('author')\
    .prefetch_related(
        'tags',
        Prefetch('comments', queryset=Comment.objects.select_related('user').order_by('-created_at')[:5])
    ).filter(status='published')

# 只加载必要的字段，避免大内容/无用字段拖累
from django.contrib.auth.models import User

# ✅ 只查username、email
light_users = User.objects.only('username', 'email')

# ✅ 排除大字段content
articles = Article.objects.defer('content')

# 批量更新比循环save快数十倍
Post.objects.filter(status='draft').update(status='archived')

# 分组聚合在数据库完成，不要在Python循环处理
from django.db.models import Count
categories = Category.objects.annotate(post_count=Count('posts'))

from django.db import connection

# 打印当前请求的所有SQL（调试用）
print(connection.queries)

from django.core.cache import cache
from django.views.decorators.cache import cache_page

# 1️⃣ 视图缓存（整个页面）
@cache_page(60 * 15)  # 缓存15分钟
def hot_products(request):
    products = Product.objects.filter(views__gt=1000)
    return render(request, 'hot_products.html', {'products': products})

# 2️⃣ 片段缓存（模板部分）
"""
{% load cache %}
{% cache 600 hot_product_sidebar request.user.id %}
    <!-- 这里的内容每10分钟更新一次，且按用户ID区分 -->
{% endcache %}
"""

# 3️⃣ 函数/方法缓存
def get_user_profile(user_id):
    key = f'profile:{user_id}'
    profile = cache.get(key)
    if not profile:
        profile = UserProfile.objects.get(user_id=user_id)
        cache.set(key, profile, 60 * 5)  # 缓存5分钟
    return profile

# 解决缓存穿透：空值缓存
def get_product(id):
    key = f'product:{id}'
    product = cache.get(key)
    if product is None:
        try:
            product = Product.objects.get(id=id)
            cache.set(key, product, 60 * 5)
        except Product.DoesNotExist:
            cache.set(key, 'empty', 60)  # 空值缓存60秒
    if product == 'empty':
        return None
    return product

# 解决缓存雪崩：随机过期时间
import random
cache.set(key, value, 60 * 5 + random.randint(0, 60))  # 加0-60秒随机偏移

# 安装依赖
# pip install celery redis

# celery.py
import os
from celery import Celery

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')
app = Celery('myproject')
app.config_from_object('django.conf:settings', namespace='CELERY')
app.autodiscover_tasks()

# settings.py
CELERY_BROKER_URL = 'redis://127.0.0.1:6379/1'
CELERY_RESULT_BACKEND = 'redis://127.0.0.1:6379/2'

# tasks.py
from celery import shared_task

@shared_task
def send_welcome_email(email):
    # 模拟耗时的邮件发送
    import time
    time.sleep(3)
    print(f'Welcome email sent to {email}')

# views.py 中调用
def register(request):
    # ... 注册逻辑
    send_welcome_email.delay(user.email)  # 异步调用，不阻塞
    return redirect('home')

# settings.py
from django.contrib.staticfiles.storage import ManifestStaticFilesStorage

STATIC_URL = '/static/'
STATIC_ROOT = BASE_DIR / 'staticfiles'
STATICFILES_STORAGE = ManifestStaticFilesStorage  # 自动添加哈希后缀，避免缓存失效

# settings.py 生产配置
STATIC_URL = 'https://cdn.yourdomain.com/static/'

# gunicorn.conf.py
bind = "127.0.0.1:8000"
workers = 2 * os.cpu_count() + 1  # CPU核心数的2倍加1
worker_class = "sync"  # I/O密集用gevent，计算密集用sync
timeout = 30
max_requests = 1000  # 重启worker，避免内存泄漏