NestJS Framework Skill

Master NestJS for building scalable, maintainable Node.js applications with TypeScript, dependency injection, and enterprise patterns.

Quick Start

NestJS app in 4 steps:

1. Create Project - nest new project-name
2. Define Modules - Organize features
3. Add Controllers - Handle requests
4. Create Services - Business logic

Core Concepts

Module Structure

// users/users.module.ts
import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';
import { UsersService } from './users.service';
import { TypeOrmModule } from '@nestjs/typeorm';
import { User } from './entities/user.entity';

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService] // Make available to other modules
})
export class UsersModule {}

Controller

// users/users.controller.ts
import { Controller, Get, Post, Body, Param, Query, UseGuards } from '@nestjs/common';
import { UsersService } from './users.service';
import { CreateUserDto } from './dto/create-user.dto';
import { JwtAuthGuard } from '../auth/guards/jwt-auth.guard';
import { ApiTags, ApiOperation, ApiBearerAuth } from '@nestjs/swagger';

@ApiTags('users')
@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Get()
  @ApiOperation({ summary: 'Get all users' })
  findAll(@Query('page') page = 1, @Query('limit') limit = 10) {
    return this.usersService.findAll(page, limit);
  }

  @Get(':id')
  findOne(@Param('id') id: string) {
    return this.usersService.findOne(id);
  }

  @Post()
  @UseGuards(JwtAuthGuard)
  @ApiBearerAuth()
  create(@Body() createUserDto: CreateUserDto) {
    return this.usersService.create(createUserDto);
  }
}

Service with Dependency Injection

// users/users.service.ts
import { Injectable, NotFoundException } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { User } from './entities/user.entity';

@Injectable()
export class UsersService {
  constructor(
    @InjectRepository(User)
    private usersRepository: Repository<User>
  ) {}

  async findAll(page: number, limit: number) {
    const [users, total] = await this.usersRepository.findAndCount({
      skip: (page - 1) * limit,
      take: limit
    });
    return { data: users, total, page, limit };
  }

  async findOne(id: string): Promise<User> {
    const user = await this.usersRepository.findOne({ where: { id } });
    if (!user) {
      throw new NotFoundException(`User #${id} not found`);
    }
    return user;
  }

  async create(createUserDto: CreateUserDto): Promise<User> {
    const user = this.usersRepository.create(createUserDto);
    return this.usersRepository.save(user);
  }
}

Learning Path

Beginner (2-3 weeks)

• ✅ NestJS CLI and project structure
• ✅ Modules, Controllers, Services
• ✅ Dependency injection basics
• ✅ Basic CRUD operations

Intermediate (4-6 weeks)

• ✅ Guards, Pipes, Interceptors
• ✅ TypeORM/Prisma integration
• ✅ JWT authentication
• ✅ Validation with class-validator

Advanced (8-12 weeks)

• ✅ Microservices with transports
• ✅ GraphQL with NestJS
• ✅ WebSockets (Gateways)
• ✅ Testing strategies

Validation with DTOs

// dto/create-user.dto.ts
import { IsEmail, IsString, MinLength, IsOptional } from 'class-validator';
import { ApiProperty } from '@nestjs/swagger';

export class CreateUserDto {
  @ApiProperty({ example: 'john@example.com' })
  @IsEmail()
  email: string;

  @ApiProperty({ example: 'John Doe' })
  @IsString()
  @MinLength(2)
  name: string;

  @ApiProperty({ example: 'password123' })
  @IsString()
  @MinLength(8)
  password: string;

  @ApiProperty({ required: false })
  @IsOptional()
  @IsString()
  avatar?: string;
}

Guards for Authentication

// auth/guards/jwt-auth.guard.ts
import { Injectable, ExecutionContext } from '@nestjs/common';
import { AuthGuard } from '@nestjs/passport';

@Injectable()
export class JwtAuthGuard extends AuthGuard('jwt') {
  canActivate(context: ExecutionContext) {
    return super.canActivate(context);
  }
}

// auth/guards/roles.guard.ts
import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { Reflector } from '@nestjs/core';

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private reflector: Reflector) {}

  canActivate(context: ExecutionContext): boolean {
    const requiredRoles = this.reflector.get<string[]>('roles', context.getHandler());
    if (!requiredRoles) return true;

    const { user } = context.switchToHttp().getRequest();
    return requiredRoles.some(role => user.roles?.includes(role));
  }
}

Exception Filters

// filters/http-exception.filter.ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';
import { Response } from 'express';

@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const status = exception.getStatus();

    response.status(status).json({
      success: false,
      statusCode: status,
      message: exception.message,
      timestamp: new Date().toISOString()
    });
  }
}

Microservices Transport

// main.ts for microservice
import { NestFactory } from '@nestjs/core';
import { Transport, MicroserviceOptions } from '@nestjs/microservices';

const app = await NestFactory.createMicroservice<MicroserviceOptions>(
  AppModule,
  {
    transport: Transport.RMQ,
    options: {
      urls: ['amqp://localhost:5672'],
      queue: 'orders_queue',
      queueOptions: { durable: true }
    }
  }
);
await app.listen();

Unit Test Template

describe('UsersService', () => {
  let service: UsersService;
  let repository: Repository<User>;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [
        UsersService,
        {
          provide: getRepositoryToken(User),
          useValue: {
            findOne: jest.fn(),
            create: jest.fn(),
            save: jest.fn()
          }
        }
      ]
    }).compile();

    service = module.get<UsersService>(UsersService);
    repository = module.get<Repository<User>>(getRepositoryToken(User));
  });

  it('should find user by id', async () => {
    const user = { id: '1', name: 'John' };
    jest.spyOn(repository, 'findOne').mockResolvedValue(user as User);

    expect(await service.findOne('1')).toEqual(user);
  });
});

Troubleshooting

Problem	Cause	Solution
Circular dependency	Module imports	Use forwardRef()
Injection token not found	Missing provider	Add to module providers
Validation not working	Missing pipe	Add ValidationPipe globally
Guards not firing	Wrong order	Use @UseGuards correctly

When to Use

Use NestJS when:

• Building enterprise Node.js applications
• Need TypeScript with strong typing
• Want dependency injection
• Building microservices
• Need OpenAPI documentation

Related Skills

• Express REST API (underlying framework)
• TypeScript (language)
• GraphQL (alternative to REST)
• Microservices (distributed systems)

Resources

• NestJS Documentation
• TypeORM Integration
• NestJS Microservices