NestJS 11 Best Practices

Quick Reference

Topic When to Use Reference

Core Architecture Modules, Providers, DI, forwardRef, custom decorators core-architecture.md

Request Lifecycle Middleware, Guards, Interceptors, Pipes, Filters request-lifecycle.md

Validation & Pipes DTOs, class-validator, ValidationPipe, transforms validation-pipes.md

Authentication JWT, Passport, Guards, Local/OAuth strategies, RBAC authentication.md

Database TypeORM, Prisma, Drizzle ORM, repository patterns database-integration.md

Testing Unit tests, E2E tests, mocking providers testing.md

OpenAPI & GraphQL Swagger decorators, resolvers, subscriptions openapi-graphql.md

Microservices TCP, Redis, NATS, Kafka patterns microservices.md

Essential Patterns

Module with Providers

@Module({ imports: [DatabaseModule], controllers: [UsersController], providers: [UsersService], exports: [UsersService], // Export for other modules }) export class UsersModule {}

Controller with Validation

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

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

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

DTO with Validation

import { IsEmail, IsString, MinLength, IsOptional } from 'class-validator';

export class CreateUserDto { @IsEmail() email: string;

@IsString() @MinLength(8) password: string;

@IsOptional() @IsString() name?: string; }

Exception Filter

@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({
  statusCode: status,
  message: exception.message,
  timestamp: new Date().toISOString(),
});

} }

Guard with JWT

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

NestJS 11 Breaking Changes

• Express v5: Wildcards must be named (e.g., *splat ), optional params use braces /:file{.:ext}

• Node.js 20+: Minimum required version

• Fastify v5: Updated adapter for Fastify users

• Dynamic Modules: Same module with identical config imported multiple times = separate instances

Common Mistakes

• Not using forwardRef() for circular deps - Causes "cannot resolve dependency" errors; wrap in forwardRef(() => ModuleName)

• Throwing plain errors instead of HttpException - Loses status codes, breaks exception filters; use throw new BadRequestException('message')

• Missing @Injectable() decorator - Provider won't be injectable; always decorate services

• Global ValidationPipe without whitelist: true

• Allows unexpected properties; set whitelist: true, forbidNonWhitelisted: true

• Importing modules instead of exporting providers - Use exports array to share providers across modules

• Async config without ConfigModule.forRoot()

• ConfigService undefined; import ConfigModule in AppModule

• Testing without overrideProvider()

• Uses real services in unit tests; mock dependencies with overrideProvider(Service).useValue(mock)

• E2E tests sharing database state - No isolation between tests; use transactions or truncate tables in beforeEach