NestJs: Chat Server in NestJs backed by MongoDB

This post will help you to create a Chat Server with NestJs + socket.io + MongoDB. We will develop the service in NestJs, expose the WebSocket gateway using socket.io & store the messages in MongoDB.
Follow the steps below:

Step#1: Create a NestJs project

I prefer to use Nest CLI for the same. If you do not have Nest CLI, download the package through NPM using the command:

$ npm install -g @nestjs/cli

To create a NestJs app (I am naming my project ‘chat-service’; give any name of your choice), open a console in your preferred folder, and run the command:

$ nest new chat-service

Create new NestJs project

Step#2: Create a Chat Module

Create a new NestJs Module “ChatModule”. This will create a folder ‘chat’ and a ChatModule (chat.module.ts) inside it. Run this command in terminal to generate a new module.

$ nest generate module chat

Generate Chat Module

Step#3: Add Typegoose dependencies

We will be using MongoDB for storing the chats and Typegoose for interacting with MongoDB. Install the required dependencies mentioned below:

$ npm install @typegoose/typegoose nestjs-typegoose
$ npm install mongoose@5.10.1
$ npm install --save-dev @types/mongoose@5.10.1

For more information on Typegoose integration with NestJs, visit the npm package here.

Step#4: Create a Chat entity for MongoDB

We will create a new Typegoose entity class for our ‘chat’ collection in MongoDB. We have kept just 3 columns as of now: message, sender & recipient.

Chat Entity

Step#5: Import TypegooseModule

To initialise TypegooseModule, we need a MongoDB server connection string (masked in the image below). I am using a free cloud hosted MongoDB service provided by MongoDB Atlas. Follow the steps here to obtain a free cloud hosted MongoDB service. We are here importing the TypegooseModule in the root module (AppModule -> app.module.ts).

Import TypegooseModule

Step#6: Create a ChatService

Next, we will create a ChatService (chat.service.ts) to do CRUD operations on the ‘chat’ collection through the injected Typegoose chat model. The service exposes 2 functions: getChats (to load all chats from the collection) & saveChat (to persist a single chat document).

Chat Service to interact with Typegoose

Step#7: Add socket.io dependencies

In this step, we will add the required socket.io dependencies to our application.

$ npm install @nestjs/platform-socket.io @nestjs/websockets
$ npm install --save-dev @types/socket.io

Step#8: Create a WebSocket gateway

We will now create a WebSocket gateway (chat.gateway.ts) to listen on ‘chat’ events. I have implemented the 3 lifecycle hooks provided by nestjs-socket.io: afterInit (when the service initialises), handleConnection (when a new client connect to the service) & handleDisconnect (when a client disconnects from the service).
handleNewMessage function subscribes to ‘chat’ events, receives and stores the chat in MongoDB & emits the new chat to ‘newChat’.

Chat Gateway

Step#9: Update the ChatModule

Finally, we need to provide ChatGateway & ChatService, and import the Typegoose chat model in ChatModule.

Update ChatModule

Step#10: Run the application

Now, let’s run the application. The application will run @ 3000 and so will the WebSocket.

$ npm run build
$ npm run start

Step#11: Verify

I use this amazing socket.io client to test my socket.io services. Let’s connect to our WebSocket and emit some chats. Here I am emitting a JSON object to match my Chat entity class.

Emit messages to ‘chat’

Verify if your chats are persisted to MongoDB.

Chats are persisted to MongoDB

Codebase:
https://github.com/sharmavikashkr/chat-service-nestjs