04-service-layer

A service layer encapsulates business rules, validations, and workflows behind a clean boundary using explicit dependency injection. It separates business logic from HTTP transport concerns, enabling controllers to remain thin while services orchestrate workflows across multiple endpoints.

Separating business rules from controllers improves reusability, testability, and independence from HTTP transport layers. By establishing clear service boundaries, you can reuse the same business logic across jobs, tests, and event handlers without duplicating transport-specific code.

Setting up dependency injection for testability requires defining explicit test seams and clean DTO/command boundaries. Injecting dependencies directly into services allows you to isolate business logic during unit testing without relying on HTTP transport mechanisms.

Yes, you can reuse a service layer across event handlers, jobs, and tests. Encapsulating business logic behind a clean use-case boundary with explicit dependencies keeps services independent of HTTP transport and accessible to multiple endpoint consumers.

The best way to orchestrate workflows across multiple endpoints is consolidating them within a dedicated service layer. This ensures end-to-end workflow orchestration remains decoupled from transport layers, allowing thin controllers to delegate business decisions efficiently.

You might avoid a service layer if your application lacks complex business rules or requires only basic transport handling without validations or orchestration. Implementing explicit dependency injection and service boundaries adds architectural overhead unnecessary for simple logic.