TypeScript
// app.module.ts
import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { ConfigModule } from '@nestjs/config';
import { UsersModule } from './users/users.module';

@Module({
  imports: [
    ConfigModule.forRoot({ isGlobal: true }),
    TypeOrmModule.forRoot({
      type: 'postgres',
      host: process.env.DB_HOST,
      port: +process.env.DB_PORT,
      username: process.env.DB_USER,
      password: process.env.DB_PASS,
      database: process.env.DB_NAME,
      autoLoadEntities: true,
      synchronize: process.env.NODE_ENV !== 'production',
    }),
    UsersModule,
  ],
})
export class AppModule {}

Progress:

• Set up module structure with proper separation of concerns
• Define entities with TypeORM decorators
• Create DTOs with class-validator
• Implement services with dependency injection
• Build controllers with proper HTTP methods
• Add authentication guards and middleware
• Configure database connections and migrations
• Implement error handling and logging

Step 1: Module Architecture

TypeScript
// users/users.module.ts
@Module({
  imports: [TypeOrmModule.forFeature([User])],
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}

Step 2: Entity Definition

TypeScript
// users/entities/user.entity.ts
@Entity()
export class User {
  @PrimaryGeneratedColumn('uuid')
  id: string;

  @Column({ unique: true })
  email: string;

  @Column()
  @Exclude()
  password: string;

  @CreateDateColumn()
  createdAt: Date;
}

Step 3: DTO Validation

TypeScript
// users/dto/create-user.dto.ts
export class CreateUserDto {
  @IsEmail()
  @IsNotEmpty()
  email: string;

  @IsString()
  @MinLength(8)
  @Matches(/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)/)
  password: string;
}

Step 4: Service Implementation

TypeScript
// users/users.service.ts
@Injectable()
export class UsersService {
  constructor(
    @InjectRepository(User)
    private usersRepository: Repository<User>,
  ) {}

  async create(createUserDto: CreateUserDto): Promise<User> {
    const hashedPassword = await bcrypt.hash(createUserDto.password, 10);
    const user = this.usersRepository.create({
      ...createUserDto,
      password: hashedPassword,
    });
    return this.usersRepository.save(user);
  }
}

Step 5: Controller Setup

TypeScript
// users/users.controller.ts
@Controller('users')
@UseGuards(JwtAuthGuard)
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Post()
  @UseInterceptors(ClassSerializerInterceptor)
  async create(@Body() createUserDto: CreateUserDto) {
    return this.usersService.create(createUserDto);
  }
}

Example 1: JWT Authentication Guard Input: Need to protect routes with JWT authentication Output:

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

  handleRequest(err, user, info) {
    if (err || !user) {
      throw err || new UnauthorizedException();
    }
    return user;
  }
}

Example 2: Global Exception Filter Input: Handle all unhandled exceptions consistently Output:

TypeScript
@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const request = ctx.getRequest();

    const status = exception instanceof HttpException 
      ? exception.getStatus() 
      : HttpStatus.INTERNAL_SERVER_ERROR;

    response.status(status).json({
      statusCode: status,
      timestamp: new Date().toISOString(),
      path: request.url,
      message: exception instanceof HttpException 
        ? exception.getResponse() 
        : 'Internal server error',
    });
  }
}