Nx NestJs | Autogenerate OpenApi/Swagger from DTO

2 min readJun 24, 2024

This is a guide on how to configure Nest/Swagger with an NX monorepo using NestJS.

Version used

Nx V19.3.1
Nestjs V10.3.9

Create our project

npx create-nx-workspace

Install @nestjs/swagger

npm install --save @nestjs/swagger

then add SwaggerModule on bootstrap()

import { Logger } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';

import { AppModule } from './app/app.module';
import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  const globalPrefix = 'api';
  app.setGlobalPrefix(globalPrefix);
  const port = process.env.PORT || 3000;

  //add SwaggerModule on bootstrap()
  const config = new DocumentBuilder().setTitle('API Documentation').setVersion('1.0').addTag('api').build();
  const document = SwaggerModule.createDocument(app, config);
  SwaggerModule.setup('swagger', app, document);
  //end

  await app.listen(port);
  Logger.log(`🚀 Application is running on: http://localhost:${port}/${globalPrefix}`);
}

bootstrap();

Apply @nestjs/swagger/plugin

Option 1: Edit webpack.config.js

Add “ transformers: [{ name: ‘@nestjs/swagger/plugin’ }]” into webpack.config.js file


const { NxAppWebpackPlugin } = require('@nx/webpack/app-plugin');
const { join } = require('path');

module.exports = {
  output: {
    path: join(__dirname, '../../dist/apps/my-app'),
  },
  plugins: [
    new NxAppWebpackPlugin({
      target: 'node',
      compiler: 'tsc',
      main: './src/main.ts',
      tsConfig: './tsconfig.app.json',
      assets: ["./src/assets"],
      optimization: false,
      outputHashing: 'none',
      transformers: [{ name: '@nestjs/swagger/plugin' }],
    })
  ],
};

Option 2: Edit project.json

You need to add the “@nestjs/swagger/plugin” into your project.json file within your application.

{
  "name": "my-app",
  "$schema": "../../node_modules/nx/schemas/project-schema.json",
  "sourceRoot": "apps/my-app/src",
  "projectType": "application",
  "tags": [],
  "targets": {
    "serve": {
      "executor": "@nx/js:node",
      "defaultConfiguration": "development",
      "options": {
        "buildTarget": "my-app:build"
      },
      "configurations": {
        "development": {
          "buildTarget": "my-app:build:development"
        },
        "production": {
          "buildTarget": "my-app:build:production"
        }
      }
    },
    "build": {
      "executor": "@nx/js:tsc",
      "outputs": [
        "{options.outputPath}"
      ],
      "options": {
        "outputPath": "dist/apps/my-app",
        "main": "apps/my-app/src/main.ts",
        "tsConfig": "apps/my-app/tsconfig.app.json",
        "transformers": [
          {
            "name": "@nestjs/swagger/plugin",
            "options": {
              "introspectComments": true
            }
          }
        ]
      }
    }
  }
}

Create API and DTO for testing

//test.dto.ts
export class TestDto {
  requirefield: string;
  optionalfield?: string;
}

//app.service.ts
import { Injectable } from '@nestjs/common';
import { TestDto } from './test.dto';

@Injectable()
export class AppService {
  getData(): TestDto {
    const test: TestDto = {
      requirefield: 'test',
    }
    return test;
  }
}

//app.controller.ts
import { Controller, Get } from '@nestjs/common';

import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get()
  getData() {
    return this.appService.getData();
  }
}