Persistent Storage made Easy: Fastro + Deno KV

Deno KV is a revolutionary key-value database built directly into the Deno runtime. It provides a simple, ACID-compliant storage solution that works seamlessly across local development and Deno Deploy.

Today, we're introducing the kvMiddleware for Fastro, making it even easier to integrate persistent storage into your handlers.

Why use Deno KV?

Traditional databases often require complex connection strings, ORMs, and external hosting. Deno KV eliminates this friction:

• Zero Config: No database to install or manage.
• Global Consistency: Automatic replication when using Deno Deploy.
• Atomic Operations: Support for transactions and atomic updates.
• TypeScript First: Full type safety for your keys and values.

Quick Start

To use KV in your Fastro application, simply register the middleware. It will inject a kv instance into the ctx object of every request.

import Fastro from "https://deno.land/x/fastro/mod.ts";
import { kvMiddleware } from "https://deno.land/x/fastro/middlewares/kv/mod.ts";

const app = new Fastro();
app.use(kvMiddleware);

app.get("/counter", async (req, ctx) => {
  const result = await ctx.kv.get(["counter"]);
  const nextValue = (result.value ?? 0) + 1;
  await ctx.kv.set(["counter"], nextValue);
  
  return { counter: nextValue };
});

await app.serve();

IMPORTANT: Make sure to run your app with the --unstable-kv flag: deno run --unstable-kv --allow-net main.ts

Persistent by Default

By default, kvMiddleware opens the default database for your environment. If you need to point to a specific database file, you can use the factory function:

import { createKvMiddleware } from "https://deno.land/x/fastro/middlewares/kv/mod.ts";

// Point to a local database file
app.use(createKvMiddleware("./my-database.db"));

100% Coverage & Reliability

Like all official Fastro middlewares, the kvMiddleware is 100% tested. We've verified its behavior in various scenarios:

• Automatic initialization on the first request.
• Efficient singleton pattern (reusing the same connection).
• Graceful error handling when the --unstable-kv flag is missing.

Check out the Source Code or dive into the Documentation to learn more.