Create NestJS Feature

Create complete feature modules following SOLID principles.

Quick Start

•Choose feature name - Singular, lowercase (e.g., users, orders, payments)
•Create folder structure in src/features/{feature}/
•Create module and register in app.module.ts
•Add configuration only if needed (keep it simple)
•Add environment variables with feature prefix (if needed)

Folder Structure Template

bash

src/features/{feature}/
├── config/                          # Optional - only if needed
│   └── {feature}.config.ts
├── entities/
│   └── {feature}.entity.ts
├── dto/
│   ├── create-{feature}.dto.ts
│   └── update-{feature}.dto.ts
├── exceptions/                      # Optional - use core exceptions when possible
│   └── {feature}-not-found.exception.ts
├── services/
│   └── {feature}.service.ts
├── controllers/
│   └── {feature}.controller.ts
├── tests/
│   └── {feature}.service.spec.ts
└── {feature}.module.ts

Keep it simple: Only create folders/files you actually need. Start minimal, add as you grow.

Step-by-Step Creation

Step 1: Configuration (Optional)

Only create if: Feature has 3+ related config properties.

typescript

// src/features/{feature}/config/{feature}.config.ts
import { registerAs } from '@nestjs/config';

export interface {Feature}Config {
  // Add feature-specific config properties
  property1: string;
  property2: number;
}

export default registerAs(
  '{feature}',  // Namespace
  (): {Feature}Config => ({
    property1: process.env.{FEATURE}_PROPERTY1 || 'default',
    property2: parseInt(process.env.{FEATURE}_PROPERTY2 || '0', 10),
  }),
);

For simple features: Access process.env directly in service. No need to over-engineer.

Step 2: Entity

typescript

// src/features/{feature}/entities/{feature}.entity.ts
import { Entity, PrimaryKey, Property } from '@mikro-orm/core';
import { BaseEntity } from '@/database/base.entity';

@Entity()
export class {Feature} extends BaseEntity {
  @PrimaryKey()
  id!: number;

  @Property()
  name!: string;

  // Add feature-specific properties
}

Step 3: DTOs

typescript

// src/features/{feature}/dto/create-{feature}.dto.ts
import { IsString, MinLength } from 'class-validator';
import { ApiProperty } from '@nestjs/swagger';

export class Create{Feature}Dto {
  @ApiProperty({ example: 'Example name' })
  @IsString()
  @MinLength(3)
  name: string;
}

Step 4: Exception (Optional)

First check: Can you use a core exception? (NotFoundException, CustomBadRequestException)

If feature-specific logic is needed:

typescript

// src/features/{feature}/exceptions/{feature}-not-found.exception.ts
import { HttpException, HttpStatus } from '@nestjs/common';
import { ExceptionTypeEnum, BaseExceptionDto } from '@/core/exceptions';

export class {Feature}NotFoundException extends HttpException {
  constructor(id: string | number) {
    const baseExceptionDto = BaseExceptionDto.CreateBaseException(
      [id.toString()],
      HttpStatus.NOT_FOUND,
      ExceptionTypeEnum.NOT_FOUND,
      `{Feature} with ID ${id} not found`,
    );
    super(baseExceptionDto, HttpStatus.NOT_FOUND);
  }
}

Step 5: Service (Single Responsibility)

typescript

// src/features/{feature}/services/{feature}.service.ts
import { Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { InjectRepository } from '@mikro-orm/nestjs';
import { EntityRepository } from '@mikro-orm/core';
import { {Feature} } from '../entities/{feature}.entity';
import { {Feature}NotFoundException } from '../exceptions/{feature}-not-found.exception';

@Injectable()
export class {Feature}Service {
  constructor(
    @InjectRepository({Feature})
    private readonly repository: EntityRepository<{Feature}>,
    private readonly configService: ConfigService,
  ) {}

  async findOne(id: number): Promise<{Feature}> {
    const entity = await this.repository.findOne({ id });
    if (!entity) {
      throw new {Feature}NotFoundException(id);
    }
    return entity;
  }
  
  // Keep methods focused - one responsibility each
}

Tip: If service gets large (>200 lines), consider splitting responsibilities into separate services.

Step 6: Controller

typescript

// src/features/{feature}/controllers/{feature}.controller.ts
import { Controller, Get, Post, Body, Param } from '@nestjs/common';
import { ApiTags, ApiOperation } from '@nestjs/swagger';
import { ApiCustomExceptionResponse } from '@/core/exceptions';
import { {Feature}Service } from '../services/{feature}.service';
import { Create{Feature}Dto } from '../dto/create-{feature}.dto';

@ApiTags('{feature}')
@Controller('{feature}')
export class {Feature}Controller {
  constructor(private readonly service: {Feature}Service) {}

  @Post()
  @ApiOperation({ summary: 'Create {feature}' })
  @ApiCustomExceptionResponse(400, 'Invalid data')
  create(@Body() dto: Create{Feature}Dto) {
    return this.service.create(dto);
  }

  @Get(':id')
  @ApiOperation({ summary: 'Get {feature} by ID' })
  @ApiCustomExceptionResponse(404, '{Feature} not found')
  findOne(@Param('id') id: string) {
    return this.service.findOne(+id);
  }
}

Step 7: Module

typescript

// src/features/{feature}/{feature}.module.ts
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { MikroOrmModule } from '@mikro-orm/nestjs';
import {feature}Config from './config/{feature}.config';  // If using config
import { {Feature} } from './entities/{feature}.entity';
import { {Feature}Service } from './services/{feature}.service';
import { {Feature}Controller } from './controllers/{feature}.controller';

@Module({
  imports: [
    // Only if using feature-specific config:
    ConfigModule.forFeature({feature}Config),
    MikroOrmModule.forFeature([{Feature}]),
  ],
  controllers: [{Feature}Controller],
  providers: [{Feature}Service],
  exports: [{Feature}Service],  // Export if other features need it
})
export class {Feature}Module {}

Step 8: Register in App Module

typescript

// src/app.module.ts
import { {Feature}Module } from './features/{feature}/{feature}.module';

@Module({
  imports: [
    // ... existing imports
    {Feature}Module,
  ],
})
export class AppModule {}

Step 9: Environment Variables (If Needed)

Add to .env.example:

bash

# ==============================================================================
# {Feature} Feature Configuration
# ==============================================================================
{FEATURE}_PROPERTY1=value
{FEATURE}_PROPERTY2=123

Checklist

SOLID Principles Applied

Single Responsibility: Each service/controller has one clear purpose Open/Closed: Use inheritance (BaseEntity) and composition Liskov Substitution: Entities can replace BaseEntity Interface Segregation: Services depend only on what they need Dependency Inversion: Depend on abstractions (use DI, inject interfaces)

Rules

✅ DO:

•Put everything in src/features/{feature}/
•Keep each class focused (Single Responsibility)
•Use dependency injection
•Use feature prefix for env vars: {FEATURE}_PROPERTY
•Use BaseEntity for entities
•Document with Swagger decorators
•Start simple, add complexity only when needed

❌ DON'T:

•Mix multiple responsibilities in one class
•Create tight coupling between features
•Use raw NestJS exceptions
•Over-engineer simple features
•Create config files for 1-2 env vars

Full Documentation

See .cursor/rules/architecture.mdc for complete architecture guidelines.