Cloudflare KV 完全指南：什么时候用 KV，什么时候用 D1？

// 写入
await env.MY_KV.put(
  'user:123',
  JSON.stringify({ name: 'Chiway', role: 'admin' }),
)
 
// 读取
const user = await env.MY_KV.get('user:123', 'json')
 
// 带过期时间写入（秒）
await env.MY_KV.put('session:abc', token, { expirationTtl: 3600 })
 
// 列出所有 key
const keys = await env.MY_KV.list({ prefix: 'user:' })
 
// 删除
await env.MY_KV.delete('user:123')

// 存储
await env.CONFIG.put(
  'feature:dark-mode',
  JSON.stringify({ enabled: true, rollout: 0.5 }),
)
 
// 读取
const feature = await env.CONFIG.get('feature:dark-mode', 'json')
if (feature?.enabled && Math.random() < feature.rollout) {
  // 启用暗色模式
}

// 创建 session
const sessionId = crypto.randomUUID()
await env.SESSIONS.put(
  `session:${sessionId}`,
  JSON.stringify({ userId: 123 }),
  {
    expirationTtl: 86400, // 24 小时过期
  },
)
 
// 验证 session
const session = await env.SESSIONS.get(`session:${sessionId}`, 'json')
if (!session) {
  return new Response('Unauthorized', { status: 401 })
}

async function getWeather(city: string, env: Env) {
  const cacheKey = `weather:${city}`
 
  // 先查缓存
  const cached = await env.CACHE.get(cacheKey, 'json')
  if (cached) return cached
 
  // 缓存未命中，请求源 API
  const response = await fetch(`https://api.weather.com/v1/${city}`)
  const data = await response.json()
 
  // 写入缓存，5 分钟过期
  await env.CACHE.put(cacheKey, JSON.stringify(data), { expirationTtl: 300 })
 
  return data
}

// 存储用户偏好
await env.PREFS.put(
  `user:${userId}:prefs`,
  JSON.stringify({
    theme: 'dark',
    language: 'zh-CN',
    timezone: 'Asia/Shanghai',
  }),
)
 
// 读取
const prefs = await env.PREFS.get(`user:${userId}:prefs`, 'json')

async function rateLimit(ip: string, env: Env): Promise<boolean> {
  const key = `ratelimit:${ip}`
  const current = parseInt((await env.LIMITS.get(key)) || '0')
 
  if (current >= 100) {
    return false // 超限
  }
 
  // 注意：这里有竞态条件，高并发下计数可能不准
  // 需要精确限流请用 Durable Objects
  await env.LIMITS.put(key, String(current + 1), { expirationTtl: 60 })
  return true
}

-- 这种查询 KV 做不了
SELECT * FROM posts WHERE author_id = 123 AND status = 'published' ORDER BY created_at DESC LIMIT 10;

SELECT posts.title, users.name
FROM posts
JOIN users ON posts.author_id = users.id
WHERE posts.created_at > date('now', '-7 days');

SELECT author_id, COUNT(*) as post_count
FROM posts
GROUP BY author_id
HAVING post_count > 10;

await env.DB.batch([
  env.DB.prepare('UPDATE accounts SET balance = balance - ? WHERE id = ?').bind(
    100,
    fromId,
  ),
  env.DB.prepare('UPDATE accounts SET balance = balance + ? WHERE id = ?').bind(
    100,
    toId,
  ),
])

async function getPost(slug: string, env: Env) {
  // 1. 先查 KV 缓存
  const cacheKey = `post:${slug}`
  const cached = await env.CACHE.get(cacheKey, 'json')
  if (cached) {
    return cached
  }
 
  // 2. 缓存未命中，查 D1
  const post = await env.DB.prepare(
    `SELECT posts.*, users.name as author_name
     FROM posts
     JOIN users ON posts.author_id = users.id
     WHERE posts.slug = ?`,
  )
    .bind(slug)
    .first()
 
  if (post) {
    // 3. 写入缓存，10 分钟过期
    await env.CACHE.put(cacheKey, JSON.stringify(post), { expirationTtl: 600 })
  }
 
  return post
}

async function updatePost(id: number, data: any, env: Env) {
  // 更新 D1
  await env.DB.prepare('UPDATE posts SET title = ?, content = ? WHERE id = ?')
    .bind(data.title, data.content, id)
    .run()
 
  // 清理相关缓存
  const post = await env.DB.prepare('SELECT slug FROM posts WHERE id = ?')
    .bind(id)
    .first()
  if (post) {
    await env.CACHE.delete(`post:${post.slug}`)
  }
}