Nestjs

---
name: nestjs
description: NestJS architecture including modules, dependency injection, guards, interceptors, and microservices patterns.
allowed-tools: Read, Write, Edit, Bash, Glob, Grep
graph:
  domains: [domain:web-development]
  specializations: [specialization:web-development]
  skillAreas: [skill-area:backend-api-design, skill-area:middleware-design]
  roles: [role:backend-engineer]
  topics: [topic:dependency-injection, topic:design-patterns]

---

# NestJS Skill

Expert assistance for building enterprise Node.js applications with NestJS.

## Capabilities

- Design modular NestJS applications
- Implement dependency injection patterns
- Create guards, pipes, and interceptors
- Build microservices architectures
- Configure Swagger/OpenAPI documentation
- Set up testing with Jest

## Usage

Invoke this skill when you need to:
- Build enterprise-grade APIs
- Implement microservices
- Create modular architecture
- Add authentication/authorization
- Generate API documentation

## Inputs

| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| moduleName | string | Yes | Module name |
| features | array | No | guards, pipes, interceptors |
| database | string | No | prisma, typeorm, mongoose |
| microservices | boolean | No | Enable microservices |

## Architecture Patterns

### Module Structure

```typescript
// src/users/users.module.ts
import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';
import { UsersService } from './users.service';
import { PrismaModule } from '../prisma/prisma.module';

@Module({
  imports: [PrismaModule],
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}
```

### Controller with DTOs

```typescript
// src/users/users.controller.ts
import {
  Controller,
  Get,
  Post,
  Put,
  Delete,
  Body,
  Param,
  Query,
  UseGuards,
  HttpCode,
  HttpStatus,
} from '@nestjs/common';
import { ApiTags, ApiOperation, ApiBearerAuth, ApiResponse } from '@nestjs/swagger';
import { UsersService } from './users.service';
import { CreateUserDto } from './dto/create-user.dto';
import { UpdateUserDto } from './dto/update-user.dto';
import { UserResponseDto } from './dto/user-response.dto';
import { PaginationDto } from '../common/dto/pagination.dto';
import { JwtAuthGuard } from '../auth/guards/jwt-auth.guard';
import { RolesGuard } from '../auth/guards/roles.guard';
import { Roles } from '../auth/decorators/roles.decorator';
import { CurrentUser } from '../auth/decorators/current-user.decorator';

@ApiTags('users')
@Controller('users')
@UseGuards(JwtAuthGuard, RolesGuard)
@ApiBearerAuth()
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Get()
  @ApiOperation({ summary: 'Get all users' })
  @ApiResponse({ status: 200, type: [UserResponseDto] })
  findAll(@Query() pagination: PaginationDto) {
    return this.usersService.findAll(pagination);
  }

  @Get(':id')
  @ApiOperation({ summary: 'Get user by ID' })
  @ApiResponse({ status: 200, type: UserResponseDto })
  findOne(@Param('id') id: string) {
    return this.usersService.findById(id);
  }

  @Post()
  @Roles('admin')
  @ApiOperation({ summary: 'Create user' })
  @ApiResponse({ status: 201, type: UserResponseDto })
  create(@Body() createUserDto: CreateUserDto) {
    return this.usersService.create(createUserDto);
  }

  @Put(':id')
  @ApiOperation({ summary: 'Update user' })
  update(@Param('id') id: string, @Body() updateUserDto: UpdateUserDto) {
    return this.usersService.update(id, updateUserDto);
  }

  @Delete(':id')
  @Roles('admin')
  @HttpCode(HttpStatus.NO_CONTENT)
  @ApiOperation({ summary: 'Delete user' })
  remove(@Param('id') id: string) {
    return this.usersService.delete(id);
  }
}

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

export class CreateUserDto {
  @ApiProperty({ example: 'John Doe' })
  @IsString()
  name: string;

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

  @ApiProperty({ minLength: 8 })
  @IsString()
  @MinLength(8)
  password: string;

  @ApiProperty({ required: false, enum: ['user', 'admin'] })
  @IsOptional()
  @IsEnum(['user', 'admin'])
  role?: string;
}
```

### Service with Dependency Injection

```typescript
// src/users/users.service.ts
import { Injectable, NotFoundException, ConflictException } from '@nestjs/common';
import { PrismaService } from '../prisma/prisma.service';
import { CreateUserDto } from './dto/create-user.dto';
import { UpdateUserDto } from './dto/update-user.dto';
import { PaginationDto } from '../common/dto/pagination.dto';
import * as bcrypt from 'bcryptjs';

@Injectable()
export class UsersService {
  constructor(private readonly prisma: PrismaService) {}

  async findAll(pagination: PaginationDto) {
    const { page = 1, limit = 10, search } = pagination;
    const skip = (page - 1) * limit;

    const [users, total] = await Promise.all([
      this.prisma.user.findMany({
        where: search ? { name: { contains: search, mode: 'insensitive' } } : undefined,
        skip,
        take: limit,
        select: {
          id: true,
          name: true,
          email: true,
          role: true,
          createdAt: true,
        },
      }),
      this.prisma.user.count({
        where: search ? { name: { contains: search, mode: 'insensitive' } } : undefined,
      }),
    ]);

    return {
      data: users,
      meta: {
        total,
        page,
        limit,
        totalPages: Math.ceil(total / limit),
      },
    };
  }

  async findById(id: string) {
    const user = await this.prisma.user.findUnique({
      where: { id },
      select: {
        id: true,
        name: true,
        email: true,
        role: true,
        createdAt: true,
      },
    });

    if (!user) {
      throw new NotFoundException(`User with ID ${id} not found`);
    }

    return user;
  }

  async create(dto: CreateUserDto) {
    const existing = await this.prisma.user.findUnique({
      where: { email: dto.email },
    });

    if (existing) {
      throw new ConflictException('Email already in use');
    }

    const hashedPassword = await bcrypt.hash(dto.password, 10);

    return this.prisma.user.create({
      data: {
        ...dto,
        password: hashedPassword,
      },
      select: {
        id: true,
        name: true,
        email: true,
        role: true,
        createdAt: true,
      },
    });
  }

  async update(id: string, dto: UpdateUserDto) {
    await this.findById(id);

    if (dto.password) {
      dto.password = await bcrypt.hash(dto.password, 10);
    }

    return this.prisma.user.update({
      where: { id },
      data: dto,
      select: {
        id: true,
        name: true,
        email: true,
        role: true,
        createdAt: true,
      },
    });
  }

  async delete(id: string) {
    await this.findById(id);
    await this.prisma.user.delete({ where: { id } });
  }
}
```

### Guards and Decorators

```typescript
// src/auth/guards/jwt-auth.guard.ts
import { Injectable, ExecutionContext } from '@nestjs/common';
import { AuthGuard } from '@nestjs/passport';
import { Reflector } from '@nestjs/core';
import { IS_PUBLIC_KEY } from '../decorators/public.decorator';

@Injectable()
export class JwtAuthGuard extends AuthGuard('jwt') {
  constructor(private reflector: Reflector) {
    super();
  }

  canActivate(context: ExecutionContext) {
    const isPublic = this.reflector.getAllAndOverride<boolean>(IS_PUBLIC_KEY, [
      context.getHandler(),
      context.getClass(),
    ]);

    if (isPublic) {
      return true;
    }

    return super.canActivate(context);
  }
}

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

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

  canActivate(context: ExecutionContext): boolean {
    const requiredRoles = this.reflector.getAllAndOverride<string[]>(ROLES_KEY, [
      context.getHandler(),
      context.getClass(),
    ]);

    if (!requiredRoles) {
      return true;
    }

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

// src/auth/decorators/roles.decorator.ts
import { SetMetadata } from '@nestjs/common';
export const ROLES_KEY = 'roles';
export const Roles = (...roles: string[]) => SetMetadata(ROLES_KEY, roles);

// src/auth/decorators/current-user.decorator.ts
import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const CurrentUser = createParamDecorator(
  (data: unknown, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);
```

### Interceptors

```typescript
// src/common/interceptors/transform.interceptor.ts
import {
  Injectable,
  NestInterceptor,
  ExecutionContext,
  CallHandler,
} from '@nestjs/common';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

export interface Response<T> {
  data: T;
  meta?: Record<string, any>;
}

@Injectable()
export class TransformInterceptor<T> implements NestInterceptor<T, Response<T>> {
  intercept(context: ExecutionContext, next: CallHandler): Observable<Response<T>> {
    return next.handle().pipe(
      map((data) => {
        if (data?.data && data?.meta) {
          return data;
        }
        return { data };
      }),
    );
  }
}
```

## Best Practices

- Use modules for feature encapsulation
- Leverage dependency injection
- Implement DTOs for validation
- Use guards for authorization
- Generate OpenAPI documentation

## Target Processes

- enterprise-api-development
- microservices-architecture
- backend-development
- nestjs-application