How do you implement a custom database query cache?

Question

Accepted Answer

**Query cache** — cache database query results.

```javascript
const Redis = require("ioredis");
const redis = new Redis();

class QueryCache {
    constructor(options = {}) {
        this.prefix = options.prefix || "query:";
        this.defaultTTL = options.ttl || 300;
    }

generateKey(query, params) {
        const hash = require("crypto")
            .createHash("md5")
            .update(JSON.stringify({ query, params }))
            .digest("hex");
        return `${this.prefix}${hash}`;
    }

async get(query, params) {
        const key = this.generateKey(query, params);
        const cached = await redis.get(key);
        return cached ? JSON.parse(cached) : null;
    }

async set(query, params, data, ttl) {
        const key = this.generateKey(query, params);
        await redis.setEx(key, ttl || this.defaultTTL, JSON.stringify(data));
    }

async invalidate(pattern) {
        const keys = await redis.keys(`${this.prefix}${pattern}`);
        if (keys.length) await redis.del(...keys);
    }
}

// Wrap database queries
const queryCache = new QueryCache({ ttl: 600 });

async function cachedQuery(query, params, options = {}) {
    const cached = await queryCache.get(query, params);
    if (cached) return cached;

const result = await db.query(query, params);
    await queryCache.set(query, params, result.rows, options.ttl);
    return result.rows;
}

// Usage
const users = await cachedQuery(
    "SELECT * FROM users WHERE active = $1",
    [true]
);

// Invalidate on write
app.post("/users", async (req, res) => {
    await db.query("INSERT INTO users ...", []);
    await queryCache.invalidate("users*");
    res.json({ ok: true });
});
```

Node.js: How do you implement a custom database query cache?