How to Create Controllers in NestJS: A Step-by-Step Guide

How to Create Controllers in NestJS: A Comprehensive Tutorial

NestJS is a powerful, progressive Node.js framework for building efficient and scalable server-side applications. Controllers in NestJS are essential components that handle incoming requests and return responses to the client. This tutorial will guide you through the process of creating controllers in NestJS using clear examples and best practices.

Prerequisites

Basic knowledge of JavaScript and TypeScript
Node.js installed on your machine
Basic understanding of RESTful APIs
Familiarity with the NestJS framework (recommended but not mandatory)
An existing NestJS project environment (or you can create one)

Step 1: Setting Up Your NestJS Project

If you don’t already have a project, start by installing the Nest CLI and creating a new project:

npm i -g @nestjs/cli
nest new my-nest-project
cd my-nest-project

This will initialize a new NestJS project with a default structure.

Step 2: Understanding Controllers in NestJS

Controllers are decorated with the @Controller() decorator. They are responsible for handling routes and HTTP requests.

A simple controller example looks like this:

import { Controller, Get } from '@nestjs/common';

@Controller('cats')
export class CatsController {
  @Get()
  findAll(): string {
    return 'This action returns all cats';
  }
}

Here:

@Controller('cats') maps this controller to the /cats route.
@Get() handles GET HTTP requests to the route /cats.
findAll() method returns a response.

Step 3: Creating Your First Controller

Use Nest CLI to generate a controller automatically with all boilerplate codes:

nest generate controller users

This command generates a users.controller.ts file with a default controller class.

Example Users Controller

import { Controller, Get, Post, Body, Param } from '@nestjs/common';

@Controller('users')
export class UsersController {
  private users = [];

  @Get()
  findAll() {
    return this.users;
  }

  @Get(':id')
  findOne(@Param('id') id: string) {
    return this.users.find(user => user.id === id);
  }

  @Post()
  create(@Body() user: any) {
    this.users.push(user);
    return user;
  }
}

Explanation:

@Get() without parameter returns the complete list of users.
@Get(':id') handles dynamic routing to fetch a user by ID.
@Post() creates a new user by reading the request body via @Body().

Step 4: Registering the Controller in Module

Make sure your controller is declared in a module, often in app.module.ts or a specific module file.

import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';

@Module({
  controllers: [UsersController],
})
export class UsersModule {}

Then import UsersModule into your root module as needed.

Step 5: Running and Testing the Controller

Launch the NestJS application:

npm run start

Test your endpoints using tools like Postman (Official site) or curl commands:

curl http://localhost:3000/users
curl -X POST http://localhost:3000/users -H "Content-Type: application/json" -d '{"id":"1","name":"John Doe"}'

Troubleshooting Tips

Controller not responding: Verify it is declared in a module’s controllers array.
404 Not Found: Check the route paths and HTTP method decorators in the controller.
Errors on @Body or @Param: Ensure you have enabled the ValidationPipe or installed body-parser middleware correctly.