NestJS Notes

NestJS Components

Fastify

NestJS mainly encapsulates application-layer functionality; the underlying network request handling framework can be swapped through an adapter. Express and Fastify are supported by default, and switching to Fastify is recommended for better performance.

import { FastifyAdapter } from '@nestjs/platform-fastify'

async function bootstrap() {
  const app = await NestFactory.create(
    AppModule,
    // Use fastify as the underlying framework
    new FastifyAdapter({
      // fastify configuration
      logger: false,
      ignoreTrailingSlash: true,
    }),
  )

  await app.listen(process.env.PORT ?? 3000)
}

You can get the Fastify instance through app.getHttpAdapter().getInstance() to use Fastify-specific features, such as fastify.register(helmet, {}) to add security policy configuration.

Swagger

Install Swagger first; it lets you send requests through a UI, saving the time spent with curl and postman. NestJS officially provides @nestjs/swagger for Swagger support, and getting started is quick:

// main.ts
async function bootstrap() {
  // Initialize the NestJS application
  const app = await NestFactory.create(AppModule)

  // Initialize Swagger
  initSwagger(app)

  // Listen on the port
  await app.listen(process.env.PORT ?? 3000)
}
bootstrap()

function initSwagger(app: INestApplication) {
  // Check whether this is the development environment
  const isDev = process.env.NODE_ENV === 'development'
  if (!isDev) {
    return
  }

  // Initialize the Swagger description information here
  const config = new DocumentBuilder()
    .setTitle('My API')
    .setDescription('My API description')
    .setVersion('1.0')
    .addTag('He110')
    .build()
  const documentFactory = () => SwaggerModule.createDocument(app, config)

  // Set the swagger URL to /swagger
  SwaggerModule.setup('swagger', app, documentFactory)
}

Prisma

Usage

1. Prisma is strongly typed; you can run npx prisma generate to generate the ORM types from the Schema that describes the data.
2. Initialize the database with npx prisma db push --force-reset, which also tests the connection status.

Environment Variables

Prisma does not support automatically switching .env files based on the runtime environment, so a feature like vite's priority-based dotenv loading needs to be implemented yourself.

MongoDB

Cannot connect to the database

Connecting to MongoDB reports Error in connector: SCRAM failure: Authentication failed.

Refer to the official documentation; with newer versions of MongoDB you need to add the ?authSource=admin query parameter to connect.

Cannot insert data

Prisma only allows transactions on a replica set when connecting to MongoDB. A local deployment generally has no replica set enabled, so you need to set up a replica set first, or connect to the hosted MongoDB Atlas.

Parameter Validation

For request parameter validation, NestJS officially recommends handling it with Pipes. If you use zod, you need to pair it with nestjs-zod.

If you follow the official zod integration tutorial, Swagger display will break and fail to read the content.

nestjs-zod provides patchNestJsSwagger, which can inject zod-defined Schemas into Swagger, avoiding the problem of duplicating data structure definitions.