Skip to main content

🧩 Clean Architecture

βœ… Overview​

A style that reorganized concepts from Hexagonal / Onion and summarized them as clear layer structures and dependency rules:

  • Entities (Enterprise Business Rules)
  • Use Cases (Application Business Rules)
  • Interface Adapters
  • Frameworks & Drivers

βœ… Problems Addressed​

  • Concepts like Hexagonal / Onion / Layered / DDD were proliferating, making differences hard to understand.
  • Wanted to organize the common idea of "Dependencies point inward" and "Domain centric".
  • Wanted more guidance on specifically what to write in which layer.

Clean Architecture can be understood as:

A unified diagram reorganizing existing styles by "Dependency Rules" and "Layers".

βœ… Basic Philosophy & Rules​

● Layer Structure​

  • Entities

    • Business rules valid across systems.
    • Close to Entities / Value Objects in DDD.

  • Use Cases

    • Application-specific use cases.
    • Input/output control, transaction boundaries, etc.

  • Interface Adapters

    • Presenter / Controller / Repository implementations, etc.
    • Convert external data formats to inner models.

  • Frameworks & Drivers

    • Web Frameworks / DB / Messaging, etc.

● Dependency Rule​

  • Dependencies point only inward (to Entities).
  • The inside does not know about the outside.
  • The outside depends on the inside's interface.

Conceptual Diagram​

The Clean Architecture diagram

Source: Robert C. Martin, β€œThe Clean Architecture”, 2012. https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html

βœ… Suitable Applications​

  • Business systems with medium to high domain complexity.
  • Products assuming long-term operation and multi-team development.
  • Backends that do not want to be tied to frameworks.
  • Development prioritizing automated tests and use-case unit tests.

❌ Unsuitable Cases​

  • Short-lived small CRUD apps.
  • When the team's experience level is low and the cost of maintaining the layer structure is higher.

If layers are introduced only in form:

  • Only the number of classes and folder hierarchy increases.
  • Dependency rules are not actually observed.

There is a danger of this happening.

βœ… History (Genealogy / Parent Styles)​

  • Proposed by Robert C. Martin (Uncle Bob).
  • A style that organized and summarized flows like Hexagonal / Onion / DDD / Layered.
  • Widely popularized as the book "Clean Architecture".

βœ… Related Styles​

βœ… Representative Frameworks​

Clean Architecture is also a concept independent of frameworks, but in practice, it is often practiced in the following technology stacks.

  • ASP.NET Core / .NET
    Many official/community templates like "Clean Architecture Template" exist.

  • Spring Boot (Java)
    Configurations clearly separating Entities / Use Cases / Interface Adapters / Frameworks & Drivers are introduced.

  • NestJS (Node.js)
    Easy to split into UseCase / Repository Interface / Adapter Implementation, making it easy to align with Clean-like structure.

βœ… Design Patterns Supporting This Style​

In Clean Architecture, multiple patterns are combined to support dependency rules and use-case centric design.

  • Adapter
    Functions as a bridge between external I/O and internal models in the Interface Adapters layer.

  • Strategy
    Expresses variations of business rules and use cases in a replaceable form.

  • Command
    Objectifies a Use Case as "one operation", clarifying input/output and transaction boundaries.

  • Facade
    Provides multiple use cases as a unified interface when viewed from the outside (UI / API).

  • Abstract Factory
    Used to assemble appropriate implementation adapters (for production / test) at runtime.

βœ… Summary​

Clean Architecture is a style that summarizes modern architectural key ideas:

  • Domain-centric design
  • Thorough dependency rules
  • Framework independence

Into a simple diagram and rule set.

Rather than "observing it perfectly", it is realistic to use it as a common language for the team to share the principle of keeping dependencies inward.