Clean Architecture

The one rule

Source-code dependencies point inward. Inner circles know nothing about outer ones.

[ Frameworks & Drivers ]   ← HTTP, DB, UI, CLI
  [ Interface Adapters ]   ← controllers, presenters, gateways
    [ Use Cases ]          ← application-specific business rules
      [ Entities ]         ← enterprise-wide business rules

If a use case imports the ORM, the rule is broken.

Ports and adapters

• Port — interface owned by the domain describing what it needs (UserRepository.find(id)).
• Adapter — implementation in the outer layer (PostgresUserRepository).
• Domain depends on ports. Composition root wires adapters to ports at startup.