Day 2

import { createClient } from 'redis';
const redis = createClient();
await redis.connect();

async function getUser(id) {
  const cacheKey = `user:${id}`;

  // 1. Check cache
  const cached = await redis.get(cacheKey);
  if (cached) {
    console.log('Cache HIT');
    return JSON.parse(cached);
  }

  // 2. Cache miss → query database
  console.log('Cache MISS');
  const user = await db.query('SELECT * FROM users WHERE id = $1', [id]);

  // 3. Store in cache with TTL
  await redis.setEx(cacheKey, 3600, JSON.stringify(user));

  return user;
}

// Invalidate cache when user is updated
async function updateUser(id, data) {
  await db.query('UPDATE users SET ...');
  await redis.del(`user:${id}`);  // invalidate
}

// Write to cache AND database together
async function createPost(data) {
  const post = await db.create(data);
  const cacheKey = `post:${post.id}`;
  await redis.setEx(cacheKey, 1800, JSON.stringify(post));
  // Also invalidate the list cache
  await redis.del('posts:all');
  return post;
}