Designing NestJS Services

When to use

• Creating new use cases
• Refactoring services that mix HTTP/DB/domain
• Moving from anemic services to OOP

Core rules

1. Application services are use-case classes, one per business intent
2. Services orchestrate domain + ports, no framework imports (no @Injectable() in domain)
3. Return Result<T,E> from use-cases, don't throw for expected failures
4. Dependencies injected via constructor
5. No HTTP/ORM imports in application services

Reference shape (TypeScript)