Controllers: Building & Routing the Users Controller (Manual + CLI)

In the last lessons you created a Users module and set up a client (Postman or any REST client) to hit your local API. Now it’s time to add your first controller.

This post explains:

• What a controller is (and why you need it)

• How to create UsersController by hand and via the Nest CLI

• How routing works with HTTP verb decorators (@Get, @Post, @Put, @Patch, @Delete)

• How to wire the controller into the module and test with Postman

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What is a controller (in NestJS)?

A controller contains your routing logic. It receives an HTTP request and picks the method to handle it based on the HTTP verb and path.

• One class (controller) can handle GET, POST, PUT, PATCH, DELETE.

• The base path for the controller comes from @Controller('...').

• Methods inside the class are matched via decorators like @Get(), @Post(), etc.

Naming (users.controller.ts) is just a convention. What makes it a controller is the @Controller() decorator.

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Create UsersController manually (great for understanding)

1) Add the file

src/users/users.controller.ts

2) Define the controller and its routes

// src/users/users.controller.ts
import { Controller, Get, Post, Put, Patch, Delete } from '@nestjs/common';

@Controller('users') // base path → /users
export class UsersController {
  @Get()
  findAll() {
    return 'GET /users';
  }

  @Post()
  create() {
    return 'POST /users';
  }

  @Put(':id')
  replace() {
    return 'PUT /users/:id';
  }

  @Patch(':id')
  update() {
    return 'PATCH /users/:id';
  }

  @Delete(':id')
  remove() {
    return 'DELETE /users/:id';
  }
}

3) Register the controller in the module

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

@Module({
  controllers: [UsersController], // ← wire it here
})
export class UsersModule {}

4) Run & smoke‑test

npm run start:dev

• GET http://localhost:3000/users → "GET /users"

• POST http://localhost:3000/users with header Content-Type: application/json → "POST /users"

If you get 404, the controller likely isn’t added to the module’s controllers: [].

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Generate the controller with the Nest CLI (quickest in real work)

Preview (safe mode):

nest g controller users --dry-run

Skip test file:

nest g controller users --no-spec --dry-run

Generate for real:

nest g controller users --no-spec

The CLI will:

• create src/users/users.controller.ts

• update src/users/users.module.ts (adds UsersController to controllers)

If you moved AppModule or use a non‑standard layout, the CLI might not auto‑wire things. Add the import manually.

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How routing works (decorators, in a nutshell)

• @Controller('users') → base path /users

• @Get() → handles GET /users

• @Post() → handles POST /users

• @Put(':id') → handles PUT /users/:id

• @Patch(':id') → handles PATCH /users/:id

• @Delete(':id') → handles DELETE /users/:id

You’ll soon add parameters (@Param()), query strings (@Query()), and bodies (@Body()), plus validation via DTOs.

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Test quickly with Postman

1. Start dev server: npm run start:dev (default port 3000)

2. GET {{base_url}}/users (e.g., http://localhost:3000/users)

3. POST {{base_url}}/users → Headers: Content-Type: application/json → Body: {} (for now)

You should see the simple strings defined in your controller. Later, we’ll connect these to real logic in a service and a database.

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Best practices (right from the start)

• Keep controllers thin. Parse inputs and delegate work to a service.

• Prefer @Body() + DTOs + ValidationPipe for clean, safe inputs.

• Keep route names resource‑oriented (/users, /users/:id).

• Consider nest g resource users later to scaffold controller + service + DTOs quickly.

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Troubleshooting

• 404 Not Found: Wrong path or controller not registered in the module.

• 415 Unsupported Media Type: Missing Content-Type: application/json on POST/PUT/PATCH.

• App didn’t restart: Ensure start:dev is running (watch mode) or restart the process.

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Up next

We’ll add real data handling:

• Read route params and query strings

• Accept and validate request bodies (DTOs + Validation Pipe)

• Introduce UsersService and move logic out of the controller