nestjs-backend-dev

NestJS Backend Development Skill

Use this skill when modifying or extending the apps/backend-api project.

1. Scaffolding Rules

When creating new features, always follow the Modular Monolith structure.

Generating a New Feature Module

Use the NestJS CLI to ensure proper wiring in app.module.ts.

# Example: Creating a 'plans' feature
cd apps/backend-api
npx nest g module modules/plans
npx nest g controller modules/plans --no-spec
npx nest g service modules/plans --no-spec

Note: We disable default spec files (--no-spec) because we prefer writing integration tests or focused unit tests later.

2. DTO & Validation Patterns

Every Controller Endpoint MUST have a dedicated DTO.

Template: Request DTO

import { IsString, IsOptional, IsInt, Min } from 'class-validator';
import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';

export class CreateItemDto {
  @ApiProperty({ description: 'The name of the item', example: 'My Item' })
  @IsString()
  name: string;

  @ApiPropertyOptional({ description: 'Optional description' })
  @IsOptional()
  @IsString()
  description?: string;
}

3. Prisma & Database Interactions

Accessing the DB

Always inject PrismaService.

constructor(private prisma: PrismaService) {}

Soft Delete Pattern

When "deleting" core business data (users, media), use update to set deletedAt.

async remove(id: number) {
  return this.prisma.media.update({
    where: { id },
    data: { deletedAt: new Date() },
  });
}

4. Queue (BullMQ) Integration

When sending jobs to the AI Engine:

1. Inject the Queue using @InjectQueue.
2. Ensure the payload matches the Python worker's expected schema.

// Constructor
constructor(@InjectQueue('transcription_queue') private transQueue: Queue) {}

// Method
async addToQueue(fileKey: string) {
  await this.transQueue.add('transcribe', {
    s3Key: fileKey,
    // ...other params
  });
}

5. Environment & Config

Access config via ConfigService, strict typed.

// BAD
const db = process.env.DATABASE_URL;

// GOOD
const db = this.configService.getOrThrow<string>('DATABASE_URL');