Clean Architecture
Clean Architecture is a software design philosophy that separates the elements of a design into ring levels. The main goal is the separation of concerns, allowing for software that is independent of frameworks, UI, databases, and external agencies.
1. The Dependency Rule
The overriding rule that makes this architecture work is the Dependency Rule:
Source code dependencies must point only inward, toward higher-level policies.
Nothing in an inner circle can know anything at all about something in an outer circle. This includes functions, classes, variables, or any other named software entity.
2. The Layers (The Onion)
The architecture is often visualized as concentric circles.
Entities (Innermost Layer)
- Encapsulate Enterprise-wide business rules.
- Least likely to change when something external changes (like page navigation or security).
- Pure logic objects.
Use Cases
- Application-specific business rules.
- Orchestrates the flow of data to and from the entities.
- Directs entities to use their Enterprise-wide business rules to achieve the goals of the use case.
Interface Adapters
- Converts data from the format most convenient for the use cases and entities, to the format most convenient for some external agency (like the Database or the Web).
- Includes Presenters, Controllers, and Gateways.
Frameworks and Drivers (Outermost Layer)
- The glue code.
- Includes the Database, the Web Framework (e.g., React, Angular, Spring), and devices.
- Generally, you don't write much code here other than glue code.
3. Benefits
- Independent of Frameworks: The architecture does not depend on the existence of some library of feature laden software. This allows you to use such frameworks as tools.
- Testable: The business rules can be tested without the UI, Database, Web Server, or any other external element.
- Independent of UI: The UI can change easily, without changing the rest of the system. A Web UI could be replaced with a console UI, for example, without changing the business rules.
- Independent of Database: You can swap out Oracle or SQL Server, for Mongo, BigTable, CouchDB, or something else. Your business rules are not bound to the database.
4. Implementation Example (Structure)
src/
domain/ # Entities (No dependencies)
User.ts
use-cases/ # Application Logic (Depends on domain)
CreateUser.ts
adapters/ # Controllers/Presenters (Depends on use-cases)
UserController.ts
UserRepositoryImpl.ts
infrastructure/ # Frameworks/Drivers (Depends on adapters)
ExpressServer.ts
PostgresDB.tsprogramming/solid-principles programming/microservices-architecture programming/software-testing-basics