Understand how to use Fastify plugin

[SkyTik]

What are you trying to achieve, or the steps to reproduce?

I'm studying Fastify and register plugin with @fastify/redis like this

app.register(redisPlugin, {
  client: initRedis(app.config.REDIS_INTERNAL__HOST, app.config.REDIS_INTERNAL__PASS),
  closeClient: true,
});

And register route:

import { FastifyInstance, FastifyPluginAsync } from "fastify";

import v1Routes from "./v1/index.js";

const routes: FastifyPluginAsync = async (fastify: FastifyInstance): Promise<void> => {
  fastify.register(v1Routes, { prefix: "/v1" });
};

export default routes;

and inside v1 route

const v1Routes: FastifyPluginAsync = async (fastify: FastifyInstance): Promise<void> => {
  fastify.register(seedlogsRoutes, { prefix: "/seedlogs" });
};

route with controller

const orderRoutes: FastifyPluginAsync = async (fastify: FastifyInstance) => {
 fastify.get("/", getOrders);
};

export default orderRoutes;

with getOrders function, I can access Redis like this:

const getOrders = async (request: FastifyRequest, reply: FastifyReply) => {
  const redis = request.server.redis;
  await redis.set("orders", "abc");
  const orders = await redis.get("orders");
  return { message: "Orders", orders };
};

But what if I want to access Redis from an inner service, how can I access Redis from the
FastifyInstance, like

const cacheOrder = async (order) => {
  await redis.set("order",order)
}

Should I init a client before passing it to the plugin and reuse it wherever does not have access to the FastifyInstance?

import redis from "./cache/redis.js"

I searched on Google but still can not find any satisfactory answer.
Many thanks

Context

• node version: 20.14.0
• fastify version: 4.28.1
• os: Mac

[metcoder95]

What do you mean exactly with an inner service?

When decorating a FastifyInstance, you can access the different decorations through the this context of the decoration.

Then, you can do things like:

fastifyInstance.decorate('service', function (..args) {
  await this.otherDecorator();
  // do your thing
})

So the reference to the main fastifyInstance is preserved and you can use it across decorators.

[SkyTik]

my flow is Route -> Controller -> Service, the Controller look like this

const getOrders = async (request: FastifyRequest, reply: FastifyReply) => {
  const redis = request.server.redis;
  await redis.set("orders", "abc");
  const orders = await redis.get("orders");
  return { message: "Orders", orders };
};

I can easily access the Redis via server, now I want to modify the Controller into this

const getOrders = async (request: FastifyRequest, reply: FastifyReply) => {
  const order = request.body;
  const newOrder = await createOrder(order);
  await cacheOrderDetail(order)
  return { message: "Orders", orders };
};

const cacheOrderDetail = (order) => {
 // how can I access Redis in this function
}

In Express, I only need to import the Redis client.

[metcoder95]

I'd say that it is mostly up to you; you can also import and reference it there directly, or follow a Dependency Injection pattern.

fastify.decorate('cacheOrderDetail', cacheOrderDetail(fastify.redis));

// later in code

fastify.cacheOrderDetail(order);

It will depend on what methodology, or principles are you following within your application structure

[SkyTik]

Still I do not understand why I need plugin if I can import the client directly in code

[climba03003]

We are not restricting developer to use the plugin, you can use the controller just like normal import.

The benefit of plugin is that,

1. Database / Resource is managed inside a single place and binded to the application lifecycle.
2. Ensure the singleton of instance
3. Encapsulation Context

I knows that you can achieve it with many different way.
The plugin only offer you one of the solution.

[SkyTik]

Thank you, I'm looking into DI to achieve my purpose.