Dependency rule, ports & adapters, NetArchTest enforcement.

Clean Architecture in .NET 9 — One Rule, Four Layers

Clean Architecture centres on the Dependency Rule: dependencies always point inward. Domain (innermost) has no dependencies. Application depends only on Domain. Infrastructure implements Application interfaces. Presentation (API) calls Application. This is the ports-and-adapters (Hexagonal) pattern. NetArchTest enforces the rules automatically. Overusing it on CRUD APIs adds cost; Vertical Slice Architecture is often a better fit.

Interactive Pipeline Flow

FoundationCore LogicProduction

🌐 Presentation — API / Controllers

Presentation layer: ASP.NET Core controllers or Minimal API endpoints. Depends on Application layer only. Never references EF Core or Infrastructure.

Architecture Diagrams

Automated architecture rule validation with NetArchTest.

Loading diagram...

Key Design Decisions

📏One rule: dependencies point inward

Domain knows nothing. Application knows Domain. Infrastructure implements Application interfaces. Presentation calls Application. That's it.

🧪Domain tests need no database

Domain entities and Application handlers can be unit-tested with no EF Core or external services. This is the key payoff of Clean Architecture.

🍕Consider Vertical Slices for CRUD

Clean Architecture shines for complex domains. For CRUD APIs, Vertical Slice Architecture (feature folders) is faster with less boilerplate.

Discussion