3. Business logic lives in a framework-agnostic service layer

Date: 2026-07-15

Status

Accepted

Context

The comparison this lab makes is only fair if the frameworks are compared on the thing they actually are: the delivery mechanism. If the reservation logic is tangled into a Laravel controller in one backend and a Go handler in another, we are comparing two different programs, not two framework idioms.

Decision

Every backend uses the same layering:

controller/handler -> use case / service -> repository (port) -> adapter (DB/cache/queue)

• Business rules live in use cases / services, with no import of the web framework.
• Repositories are ports (interfaces). Concrete adapters (Postgres, Redis, broker) are injected. The domain depends on the abstraction; the driver depends on the domain. Dependency inversion, applied rather than quoted.
• Controllers are thin: parse, validate, call a use case, serialize. A controller that contains a business rule is a bug.

Consequences

• Use cases are unit-testable with in-memory fakes and no running infrastructure.
• The interesting comparison across backends is narrowed to how each framework does routing, validation, and dependency injection, which is exactly the comparison we want.
• More files and more indirection than a fat-controller approach. For a teaching codebase this is the point; for a weekend script it would be overkill, and we say so in the recipes.