hjemmesidekongen/nestjs-patterns

NestJS Patterns

NestJS is Angular-influenced — modules, DI, and decorators are the core model. Work with the framework's conventions; fighting them creates unmaintainable code.

Module Organization

Feature modules own everything inside their boundary: controller, service, repository, DTOs. CoreModule handles app-wide singletons (config, logger, DB connection). SharedModule exports reusable utilities with no circular dependencies.

Keep AppModule thin — it imports feature modules and wires global middleware only.

Request Lifecycle

Middleware → Guards → Interceptors (pre) → Pipes → Handler → Interceptors (post) → Exception Filters

Order matters. Guards run before pipes. Interceptors wrap the entire handler. Exception filters catch what escapes guards and handlers both.

Decorator Patterns

Use custom decorators to extract repeated logic from handlers: @CurrentUser(), @Roles(), @Public(). Keep handlers thin — they should read like a spec, not an implementation.

Combine @UseGuards(), @UseInterceptors(), and @UsePipes() at the controller level when they apply to all routes. Route-level decorators only when behavior diverges.

Testing Approach

Unit tests: Test.createTestingModule() with mocked providers. Mock at the service boundary, not inside services. Test one class per file.

E2E tests: @nestjs/testing with supertest. Spin up the full app, hit real endpoints, use a test DB or in-memory store. Cover auth flows and request validation end-to-end.

See references/process.md for module patterns, DI, guards, interceptors, pipes, exception filters, middleware, microservices basics, CQRS, and anti-patterns.