lcbp3/.agents/skills/nestjs-best-practices/SKILL.md

name, description, license, metadata

name	description	license	metadata
nestjs-best-practices	NestJS best practices and architecture patterns for building production-ready applications. This skill should be used when writing, reviewing, or refactoring NestJS code to ensure proper patterns for modules, dependency injection, security, and performance.	MIT	author version Kadajett 1.1.0

NestJS Best Practices

Comprehensive best practices guide for NestJS applications. Contains 40 rules across 10 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

• Writing new NestJS modules, controllers, or services
• Implementing authentication and authorization
• Reviewing code for architecture and security issues
• Refactoring existing NestJS codebases
• Optimizing performance or database queries
• Building microservices architectures

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Architecture	CRITICAL	arch-
2	Dependency Injection	CRITICAL	di-
3	Error Handling	HIGH	error-
4	Security	HIGH	security-
5	Performance	HIGH	perf-
6	Testing	MEDIUM-HIGH	test-
7	Database & ORM	MEDIUM-HIGH	db-
8	API Design	MEDIUM	api-
9	Microservices	MEDIUM	micro-
10	DevOps & Deployment	LOW-MEDIUM	devops-

Quick Reference

1. Architecture (CRITICAL)

• arch-avoid-circular-deps - Avoid circular module dependencies
• arch-feature-modules - Organize by feature, not technical layer
• arch-module-sharing - Proper module exports/imports, avoid duplicate providers
• arch-single-responsibility - Focused services over "god services"
• arch-use-repository-pattern - Abstract database logic for testability
• arch-use-events - Event-driven architecture for decoupling

2. Dependency Injection (CRITICAL)

• di-avoid-service-locator - Avoid service locator anti-pattern
• di-interface-segregation - Interface Segregation Principle (ISP)
• di-liskov-substitution - Liskov Substitution Principle (LSP)
• di-prefer-constructor-injection - Constructor over property injection
• di-scope-awareness - Understand singleton/request/transient scopes
• di-use-interfaces-tokens - Use injection tokens for interfaces

3. Error Handling (HIGH)

• error-use-exception-filters - Centralized exception handling
• error-throw-http-exceptions - Use NestJS HTTP exceptions
• error-handle-async-errors - Handle async errors properly

4. Security (HIGH)

• security-auth-jwt - Secure JWT authentication
• security-validate-all-input - Validate with class-validator
• security-use-guards - Authentication and authorization guards
• security-sanitize-output - Prevent XSS attacks
• security-rate-limiting - Implement rate limiting

5. Performance (HIGH)

• perf-async-hooks - Proper async lifecycle hooks
• perf-use-caching - Implement caching strategies
• perf-optimize-database - Optimize database queries
• perf-lazy-loading - Lazy load modules for faster startup

6. Testing (MEDIUM-HIGH)

• test-use-testing-module - Use NestJS testing utilities
• test-e2e-supertest - E2E testing with Supertest
• test-mock-external-services - Mock external dependencies

7. Database & ORM (MEDIUM-HIGH)

• db-hybrid-identifier - CRITICAL ADR-019: INT PK + UUID public API
• db-avoid-n-plus-one - HIGH N+1 query prevention
• db-use-transactions - HIGH Transaction management
• db-no-typeorm-migrations - CRITICAL ADR-009: No TypeORM migrations - use SQL files

8. API Design (MEDIUM)

• api-use-dto-serialization - DTO and response serialization
• api-use-interceptors - Cross-cutting concerns
• api-versioning - API versioning strategies
• api-use-pipes - Input transformation with pipes

9. Microservices (MEDIUM)

• micro-use-patterns - Message and event patterns
• micro-use-health-checks - Health checks for orchestration
• micro-use-queues - Background job processing

10. DevOps & Deployment (LOW-MEDIUM)

• devops-use-config-module - Environment configuration
• devops-use-logging - Structured logging
• devops-graceful-shutdown - Zero-downtime deployments

NAP-DMS Project-Specific Rules (MUST FOLLOW)

These rules override general NestJS best practices for the NAP-DMS project:

ADR-009: No TypeORM Migrations

• ห้ามสร้างไฟล์ migration ของ TypeORM
• แก้ไข schema โดยตรงที่: specs/03-Data-and-Storage/lcbp3-v1.8.0-schema-02-tables.sql
• ใช้ n8n workflow สำหรับ data migration ถ้าจำเป็น

ADR-019: Hybrid Identifier Strategy (CRITICAL)

@Entity()
export class Project {
  @PrimaryGeneratedColumn()
  @Exclude() // ห้ามส่งออกทาง API
  id: number; // INT AUTO_INCREMENT - internal only

  @Column({ type: 'uuid' })
  @Expose({ name: 'id' }) // ส่งออกเป็น 'id' ทาง API
  publicId: string; // UUIDv7 - public API identifier
}

Two-Phase File Upload

// Phase 1: Upload to temp
@Post('upload')
async uploadFile(@UploadedFile() file: Express.Multer.File) {
  await this.virusScan(file);
  const tempId = await this.fileStorage.saveToTemp(file);
  return { temp_id: tempId, expires_at: addHours(new Date(), 24) };
}

// Phase 2: Commit in transaction
async createEntity(dto: CreateDto, tempIds: string[]) {
  return this.dataSource.transaction(async (manager) => {
    const entity = await manager.save(Entity, dto);
    await this.fileStorage.commitFiles(tempIds, entity.id, manager);
    return entity;
  });
}

Idempotency Requirement

• ทุก POST/PUT/PATCH ที่สำคัญต้องมี Idempotency-Key header
• ใช้ IdempotencyInterceptor ที่มีอยู่แล้ว

Document Numbering (Double-Lock)

async generateNextNumber(context: NumberingContext): Promise<string> {
  const lockKey = `doc_num:${context.projectId}:${context.typeId}`;
  const lock = await this.redisLock.acquire(lockKey, 3000);

  try {
    const counter = await this.counterRepo.findOne({
      where: context,
      lock: { mode: 'optimistic' },
    });
    counter.last_number++;
    return this.formatNumber(await this.counterRepo.save(counter));
  } finally {
    await lock.release();
  }
}

Anti-Patterns (ห้ามทำ)

• ❌ ใช้ SQL Triggers สำหรับ business logic
• ❌ ใช้ .env ใน production (ใช้ Docker ENV)
• ❌ ใช้ any type (strict mode enforced)
• ❌ ใช้ console.log (ใช้ NestJS Logger)
• ❌ สร้างตาราง routing แยก (ใช้ Workflow Engine)

---

Read individual rule files for detailed explanations and code examples:

rules/arch-avoid-circular-deps.md
rules/security-validate-all-input.md
rules/_sections.md

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md