backend-dev-guidelines

Structure your Express backend using a layered architecture: Routes handle HTTP requests, Controllers orchestrate logic, Services encapsulate business rules, and Repositories manage database access. This separation of concerns makes code testable, maintainable, and easier to scale as your API grows.

Implement middleware in a pipeline for validation, authentication, and error handling. Use custom AppError classes with a global error-handling middleware to standardize responses. This ensures consistent, informative error messages across all routes and simplifies debugging.

Use repositories to abstract database operations from service logic. A repository pattern with Prisma or similar tools isolates data access, making services database-agnostic and testable. Services call repositories instead of directly querying the database.

Yes. Type-safe Data Transfer Objects and validators prevent invalid data from reaching your services. TypeScript DTOs provide compile-time safety, while runtime validators catch malformed requests, reducing bugs and improving API reliability.

Yes. The layered architecture with Routes, Controllers, Services, and Repositories scales across multiple entities. Each entity follows the same pattern: define routes, implement controllers and services for business logic, and use repositories for database operations.

Test each layer independently: unit test Services and Repositories with mocked dependencies, integration test Controllers with test databases, and end-to-end test Routes. The layered architecture makes isolation and mocking straightforward, improving test reliability.