NestJS Architecture Expert

Priority: P0 (CRITICAL)

Design decoupled, testable modules with clear boundaries.

Workflow: Create a New Feature Module

1. Generate module — nest g module users creates the feature module.
2. Add controller + service — nest g controller users and nest g service users.
3. Register dependencies — Import TypeOrmModule.forFeature([User]) in the module.
4. Validate inputs — Apply class-validator decorators on all DTOs.
5. Check circular deps — Run madge --circular src/ to verify no cycles.

Module Structure Example

See implementation examples

Implementation Guidelines

• Modules: Feature Modules (Auth) vs Core (Config/DB) vs Shared (Utils).
• Controllers: Thin controllers, fat services. Verify DTOs here.
• Services: Business logic only. Use Repository pattern for DB.
• Config: Use @nestjs/config, never process.env directly.

Architecture Checklist (Mandatory)

• Circular Deps: Are there any circular dependencies? (Use madge).
• Env Validation: Is Joi/Zod schema used for env vars?
• Exception Filters: Are global filters catching unhandled errors?
• DTO Validation: Are class-validator decorators on all inputs?
• Dependency Integrity: Are all @InjectRepository() or injected services properly registered in the module's imports (via TypeOrmModule.forFeature) or providers?

Anti-Patterns

• No Global Scope: Avoid global pipes/guards unless truly universal.
• No Direct Entity: Don't return ORM entities; return DTOs.
• No Business in Controller: Move logic to Service.
• No Manual Instantiation: Use DI, never new Service().

References

• Advanced Patterns
• Dynamic Modules