《TypeScript编程实战》8.1 缓存层次与键设计

import { LRUCache } from "lru-cache";

type Dict = Map<string, string>;

// 单实例内缓存，最多 500 个键，TTL 60 秒兜底
const dictCache = new LRUCache<string, Dict>({
  max: 500,
  ttl: 60_000,
  // 允许过期后返回旧值，同时后台刷新（stale-while-revalidate）
  allowStale: true,
  updateAgeOnGet: false,
});

export async function getDict(name: string): Promise<Dict> {
  const cached = dictCache.get(name);
  if (cached) return cached; // 命中，0 次网络往返

  const fresh = await loadDictFromDb(name);
  dictCache.set(name, fresh);
  return fresh;
}

// 反例：先写库再 set 缓存
await db.update({ id, value: v });       // t1
await redis.set(key, v);    // t2 —— 若另一请求在 t1/t2 之间也写了库并先 set，
                            //        这里会用更旧的值覆盖更新的值

// 命名空间 : 版本 : 实体 : 主键 : 可选限定
// app:v2:product:10086
// app:v2:product:10086:locale=zh-CN
// app:v2:order:user:42:page:1

type Namespace = "app" | "session" | "rate";
type Version = `v${number}`;

/** 实体键：ns:vN:<entity>:<id> */
type EntityKey<E extends string> = `${Namespace}:${Version}:${E}:${string}`;

function entityKey<E extends string>(entity: E, id: string | number): EntityKey<E> {
  // 运行时仍要防注入：id 里出现 ":" 会破坏键结构
  if (String(id).includes(":")) {
    throw new Error(`cache key id must not contain ':' (got ${id})`);
  }
  return `app:v1:${entity}:${id}` as EntityKey<E>;
}

const k1 = entityKey("product", 10086);
//   ^? const k1: "app:v1:product:${string}"

const k2 = entityKey("product", "100:86");
//   ^? 运行时报错：cache key id must not contain ':' (got 100:86)

const a = JSON.stringify({ page: 1, size: 20 });
const b = JSON.stringify({ size: 20, page: 1 });
console.log(a === b); // false —— 同样的查询，两个不同的键

type Primitive = string | number | boolean | null;

function stableKey(input: Record<string, Primitive | undefined>): string {
  return Object.keys(input)
    .filter((k) => input[k] !== undefined) // 剔除 undefined，避免 null 与缺省混淆
    .sort()
    .map((k) => {
      const v = input[k];
      // 浮点必须先规范化精度，否则 0.1+0.2 会算出不同键
      const normalized =
        typeof v === "number" ? Number(v.toFixed(6)) : v;
      return `${k}=${String(normalized)}`;
    })
    .join("&");
}

console.log(stableKey({ page: 1, size: 20 }));
// "page=1&size=20"
console.log(stableKey({ size: 20, page: 1 }));
// "page=1&size=20" —— 与上一行完全一致
console.log(stableKey({ q: "TypeScript 教程", page: 1 }));
// "page=1&q=TypeScript 教程"

export const CacheKeys = {
  product: {
    detail: (id: number) => `app:v3:product:${id}` as const,
    list: (q: { page: number; size: number; sort: string }) =>
      `app:v3:product:list:${stableKey(q)}` as const,
  },
  user: {
    profile: (id: number) => `app:v3:user:${id}:profile` as const,
    perms: (id: number) => `app:v3:user:${id}:perms` as const,
  },
} satisfies Record<string, Record<string, (...args: never[]) => string>>;

CacheKeys.product.detail(10086); // "app:v3:product:10086"

async function invalidateProduct(redis: Redis, id: number) {
  // 详情键可以精确删除
  await redis.del(CacheKeys.product.detail(id));
  // 列表键基数未知，用「版本号自增」代替遍历删除：
  // 把列表键里的 v3 换成动态版本，即可一次性让旧列表全部失效
  await redis.incr("app:version:product:list");
}

SyntaxError: Unexpected token 'o', "old-shape" is not valid JSON
    at JSON.parse (<anonymous>)
    at RedisCodec.decode (/app/src/cache/codec.ts:24:18)