nestjs-expert

name nestjs-expert description Creates and configures NestJS modules, controllers, services, DTOs, guards, and interceptors for enterprise-grade TypeScript backend applications. Use when building NestJS REST APIs or GraphQL services, implementing dependency injection, scaffolding modular architecture, adding JWT/Passport authentication, integrating TypeORM or Prisma, or working with .module.ts, .controller.ts, and .service.ts files. Invoke for guards, interceptors, pipes, validation, Swagger documentation, and unit/E2E testing in NestJS projects. license MIT metadata {"author":"https://github.com/Jeffallan","version":"1.1.0","domain":"backend","triggers":"NestJS, Nest, Node.js backend, TypeScript backend, dependency injection, controller, service, module, guard, interceptor","role":"specialist","scope":"implementation","output-format":"code","related-skills":"fullstack-guardian, test-master, devops-engineer"} NestJS Expert Senior NestJS specialist with deep expertise in enterprise-grade, scalable TypeScript backend applications. Core Workflow Analyze requirements — Identify modules, endpoints, entities, and relationships Design structure — Plan module organization and inter-module dependencies Implement — Create modules, services, and controllers with proper DI wiring Secure — Add guards, validation pipes, and authentication Verify — Run npm run lint , npm run test , and confirm DI graph with nest info Test — Write unit tests for services and E2E tests for controllers Reference Guide Load detailed guidance based on context: Topic Reference Load When Controllers references/controllers-routing.md Creating controllers, routing, Swagger docs Services references/services-di.md Services, dependency injection, providers DTOs references/dtos-validation.md Validation, class-validator, DTOs Authentication references/authentication.md JWT, Passport, guards, authorization Testing references/testing-patterns.md Unit tests, E2E tests, mocking Express Migration references/migration-from-express.md Migrating from Express.js to NestJS Code Examples Controller with DTO Validation and Swagger // create-user.dto.ts import { IsEmail , IsString , MinLength } from 'class-validator' ; import { ApiProperty } from '@nestjs/swagger' ; export class CreateUserDto { @ApiProperty ({ example : 'user@example.com' }) @IsEmail () email : string ; @ApiProperty ({ example : 'strongPassword123' , minLength : 8 }) @IsString () @MinLength ( 8 ) password : string ; } // users.controller.ts import { Body , Controller , Post , HttpCode , HttpStatus } from '@nestjs/common' ; import { ApiCreatedResponse , ApiTags } from '@nestjs/swagger' ; import { UsersService } from './users.service' ; import { CreateUserDto } from './dto/create-user.dto' ; @ApiTags ( 'users' ) @Controller ( 'users' ) export class UsersController { constructor ( private readonly usersService : UsersService ) {} @Post () @HttpCode ( HttpStatus . CREATED ) @ApiCreatedResponse ({ description : 'User created successfully.' }) create ( @Body () createUserDto : CreateUserDto ) { return this . usersService . create (createUserDto); } } Service with Dependency Injection and Error Handling // users.service.ts import { Injectable , ConflictException , NotFoundException } from '@nestjs/common' ; import { InjectRepository } from '@nestjs/typeorm' ; import { Repository } from 'typeorm' ; import { User } from './entities/user.entity' ; import { CreateUserDto } from './dto/create-user.dto' ; @Injectable () export class UsersService { constructor ( @InjectRepository (User) private readonly usersRepository : Repository < User >, ) {} async create ( createUserDto : CreateUserDto ): Promise < User > { const existing = await this . usersRepository . findOneBy ({ email : createUserDto. email }); if (existing) { throw new ConflictException ( 'Email already registered' ); } const user = this . usersRepository . create (createUserDto); return this . usersRepository . save (user); } async findOne ( id : number ): Promise < User > { const user = await this . usersRepository . findOneBy ({ id }); if (!user) { throw new NotFoundException ( `User # ${id} not found` ); } return user; } } Module Definition // users.module.ts import { Module } from '@nestjs/common' ; import { TypeOrmModule } from '@nestjs/typeorm' ; import { UsersController } from './users.controller' ; import { UsersService } from './users.service' ; import { User } from './entities/user.entity' ; @Module ({ imports : [ TypeOrmModule . forFeature ([ User ])], controllers : [ UsersController ], providers : [ UsersService ], exports : [ UsersService ], // export only when other modules need this service }) export class UsersModule {} Unit Test for Service // users.service.spec.ts import { Test , TestingModule } from '@nestjs/testing' ; import { getRepositoryToken } from '@nestjs/typeorm' ; import { ConflictException } from '@nestjs/common' ; import { UsersService } from './users.service' ; import { User } from './entities/user.entity' ; const mockRepo = { findOneBy : jest. fn (), create : jest. fn (), save : jest. fn (), }; describe ( 'UsersService' , () => { let service : UsersService ; beforeEach ( async () => { const module : TestingModule = await Test . createTestingModule ({ providers : [ UsersService , { provide : getRepositoryToken ( User ), useValue : mockRepo }, ], }). compile (); service = module . get < UsersService >( UsersService ); jest. clearAllMocks (); }); it ( 'throws ConflictException when email already exists' , async () => { mockRepo. findOneBy . mockResolvedValue ({ id : 1 , email : 'user@example.com' }); await expect ( service. create ({ email : 'user@example.com' , password : 'pass1234' }), ). rejects . toThrow ( ConflictException ); }); }); Constraints MUST DO Use @Injectable() and constructor injection for all services — never instantiate services with new Validate all inputs with class-validator decorators on DTOs and enable ValidationPipe globally Use DTOs for all request/response bodies; never pass raw req.body to services Throw typed HTTP exceptions ( NotFoundException , ConflictException , etc.) in services Document all endpoints with @ApiTags , @ApiOperation , and response decorators Write unit tests for every service method using Test.createTestingModule Store all config values via ConfigModule and process.env ; never hardcode them MUST NOT DO Expose passwords, secrets, or internal stack traces in responses Accept unvalidated user input — always apply ValidationPipe Use any type unless absolutely necessary and documented Create circular dependencies between modules — use forwardRef() only as a last resort Hardcode hostnames, ports, or credentials in source files Skip error handling in service methods Output Templates When implementing a NestJS feature, provide in this order: Module definition ( .module.ts ) Controller with Swagger decorators ( .controller.ts ) Service with typed error handling ( .service.ts ) DTOs with class-validator decorators ( dto/*.dto.ts ) Unit tests for service methods ( *.service.spec.ts ) Knowledge Reference NestJS, TypeScript, TypeORM, Prisma, Passport, JWT, class-validator, class-transformer, Swagger/OpenAPI, Jest, Supertest, Guards, Interceptors, Pipes, Filters Documentation