Lesson 4: Controllers and Routing in NestJS

NestJS: From Basics to Advanced

Part 1: NestJS Platform

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1. What is a Controller?

Controllers are responsible for processing incoming requests and return responses. responses for clients. Routing mechanism decides which controller handles which request based on URL path and HTTP method.

import { Controller, Get, Post, Put, Patch, Delete } from '@nestjs/common';

@Controller('products')  // Base route: /products
export class ProductsController {
  
  @Get()           // GET    /products
  findAll() { return 'Tất cả sản phẩm'; }

  @Get(':id')      // GET    /products/123
  findOne() { return 'Một sản phẩm'; }

  @Post()          // POST   /products
  create() { return 'Tạo sản phẩm'; }

  @Put(':id')      // PUT    /products/123
  replace() { return 'Thay thế sản phẩm'; }

  @Patch(':id')    // PATCH  /products/123
  update() { return 'Cập nhật sản phẩm'; }

  @Delete(':id')   // DELETE /products/123
  remove() { return 'Xóa sản phẩm'; }
}

2. Access Request Object

Parameter Decorators

import {
  Controller, Get, Post, Param, Query, Body,
  Headers, Ip, Req, Res, HttpCode, Header,
} from '@nestjs/common';
import { Request, Response } from 'express';

@Controller('users')
export class UsersController {
  
  // Route Parameters
  @Get(':id')
  findOne(@Param('id') id: string) {         // /users/42 → id = '42'
    return `User #${id}`;
  }

  // Multiple Route Params
  @Get(':userId/posts/:postId')
  findUserPost(
    @Param('userId') userId: string,
    @Param('postId') postId: string,
  ) {
    return `User ${userId}, Post ${postId}`;
  }

  // Query Parameters
  @Get()
  findAll(
    @Query('page') page: number = 1,          // /users?page=2
    @Query('limit') limit: number = 10,       // /users?page=2&limit=20
    @Query('search') search?: string,         // /users?search=john
    @Query() allQuery: Record<string, any>,   // Tất cả query params
  ) {
    return { page, limit, search };
  }

  // Request Body
  @Post()
  create(@Body() body: CreateUserDto) {       // Full body
    return body;
  }

  @Post('partial')
  createPartial(@Body('name') name: string) { // Chỉ lấy field 'name'
    return { name };
  }

  // Headers
  @Get('info')
  getInfo(
    @Headers('authorization') auth: string,
    @Headers('user-agent') userAgent: string,
    @Ip() ip: string,
  ) {
    return { auth, userAgent, ip };
  }

  // Full Request/Response objects (ít dùng)
  @Get('raw')
  getRaw(@Req() req: Request, @Res() res: Response) {
    res.status(200).json({ url: req.url, method: req.method });
  }
}

Mapping between NestJS Decorators and Express

NestJS Decorator	Express equivalent
@Req()	req
@Res()	res
@Param(key)	req.params[key]
@Query(key)	req.query[key]
@Body(key)	req.body[key]
@Headers(key)	req.headers[key]
@Ip()	req.ip
@Session()	req.session

3. Response Handling

Standard Approach (recommended)

@Controller('products')
export class ProductsController {

  // Return object → tự động serialize thành JSON
  @Get()
  findAll(): Product[] {
    return [{ id: 1, name: 'Laptop' }];
    // Response: 200 OK, Content-Type: application/json
  }

  // Return string → plain text
  @Get('health')
  health(): string {
    return 'OK';
    // Response: 200 OK, Content-Type: text/html
  }

  // Return Promise → NestJS tự await
  @Get('async')
  async findAsync(): Promise<Product[]> {
    return await this.productService.findAll();
  }

  // Return Observable → NestJS tự subscribe
  @Get('stream')
  findStream(): Observable<Product[]> {
    return this.productService.findAllStream();
  }
}

Custom Status Codes

import { HttpCode, HttpStatus } from '@nestjs/common';

@Post()
@HttpCode(HttpStatus.CREATED)  // 201
create(@Body() dto: CreateProductDto) {
  return this.productService.create(dto);
}

@Delete(':id')
@HttpCode(HttpStatus.NO_CONTENT)  // 204
remove(@Param('id') id: string) {
  this.productService.remove(id);
}

Custom Response Headers

@Get()
@Header('Cache-Control', 'max-age=3600')
@Header('X-Custom-Header', 'NestJS')
findAll() {
  return this.productService.findAll();
}

Redirects

import { Redirect } from '@nestjs/common';

@Get('old-page')
@Redirect('/new-page', 301)  // Permanent redirect
oldPage() {}

// Dynamic redirect
@Get('docs')
@Redirect('https://docs.nestjs.com', 302)
getDocs(@Query('version') version: string) {
  if (version === 'v11') {
    return { url: 'https://docs.nestjs.com/v11' };
  }
  // Nếu không return gì, dùng URL mặc định
}

4. Route Wildcards & Pattern Matching

// Wildcard routes
@Get('ab*cd')   // Matches: abcd, ab_cd, abecd, ab123cd,...
findWild() {
  return 'This route uses a wildcard';
}

// Regex-based param (NestJS dùng path-to-regexp)
@Get(':id(\\d+)')   // Chỉ match số: /products/123 ✓, /products/abc ✗
findOne(@Param('id') id: string) {
  return `Product #${id}`;
}

5. DTOs — Data Transfer Objects

// src/products/dto/create-product.dto.ts
export class CreateProductDto {
  name: string;
  description: string;
  price: number;
  category: string;
  inStock: boolean;
}

// src/products/dto/update-product.dto.ts
import { PartialType } from '@nestjs/mapped-types';
import { CreateProductDto } from './create-product.dto';

// PartialType tạo class mới với tất cả fields optional
export class UpdateProductDto extends PartialType(CreateProductDto) {}

// Sử dụng
@Post()
create(@Body() dto: CreateProductDto) {
  // TypeScript đảm bảo dto có đúng shape
  return this.service.create(dto);
}

@Patch(':id')
update(@Param('id') id: string, @Body() dto: UpdateProductDto) {
  return this.service.update(+id, dto);
}

6. API Versioning

// main.ts — Bật versioning
import { VersioningType } from '@nestjs/common';

const app = await NestFactory.create(AppModule);
app.enableVersioning({
  type: VersioningType.URI,  // /v1/users, /v2/users
  // type: VersioningType.HEADER,  // Header: X-API-Version: 1
  // type: VersioningType.MEDIA_TYPE,  // Accept: application/json;v=1
});

// Controller
@Controller({ path: 'users', version: '1' })
export class UsersV1Controller {
  @Get()
  findAll() { return 'V1 users'; }
}

@Controller({ path: 'users', version: '2' })
export class UsersV2Controller {
  @Get()
  findAll() { return 'V2 users with pagination'; }
}

// Per-route versioning
@Controller('users')
export class UsersController {
  @Version('1')
  @Get()
  findAllV1() { return 'V1'; }

  @Version('2')
  @Get()
  findAllV2() { return 'V2'; }
}

7. Summary

• Controllers handle HTTP requests, marked with @Controller()
• Parameter Decorators: @Param(), @Query(), @Body(), @Headers()
• Response: Return object (JSON), string (text), or Promise/Observable
• DTOs: Class defines the shape of data, used PartialType for updates
• Versioning: URI, Header or Media Type

The next article will explore Providers and Dependency Injection — the core mechanism of NestJS.