🏗️ Clean Architecture Principles

Definition:

Clean Architecture is a software design approach that separates concerns into layers, making systems maintainable, testable, and flexible.

It emphasizes independence of frameworks, UI, databases, and external agencies.

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1️⃣ Core Principles

a) Separation of Concerns

• Each part of the system handles only one responsibility.
• Avoid mixing business logic, UI, and database access in the same module.
• Makes code easier to understand, maintain, and test.

Example:

UI Layer: Handles user input
Business Layer: Processes business rules
Data Layer: Reads/writes database

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b) Layered Architecture

• System is divided into distinct layers, each with a specific role.

Typical Layers in Clean Architecture:

1. Entities (Core / Domain layer)

   • Business rules, core objects, validations
   • Independent of frameworks

2. Use Cases / Application layer

   • Orchestrates business rules for specific workflows
   • Implements application-specific logic

3. Interface / Adapter layer

   • Converts data between external systems and core logic
   • Examples: Controllers, Presenters, Gateways

4. Infrastructure / Framework layer

   • Database, Web frameworks, External APIs
   • Should not affect core business logic

Flow Example:

UI → Application (Use Cases) → Domain (Entities) → Infrastructure (DB/API)

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c) Modularity

• The system is divided into modules with well-defined responsibilities.
• Modules communicate through interfaces, not concrete implementations.
• Encourages reuse and easy replacement of components.

Example:

• Payment module → only handles payments
• Notification module → only handles email/SMS

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d) Dependency Rule

• Source code dependencies point inward (toward the core domain).
• Outer layers can depend on inner layers, but inner layers must not depend on outer layers.

[Infrastructure / DB / UI] → [Use Cases] → [Entities]

• Inner layers remain independent of frameworks and easy to test.

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2️⃣ Benefits

• Testability: Business logic can be tested without UI or DB.
• Maintainability: Changes in outer layers don’t affect core logic.
• Flexibility: Easy to replace frameworks, databases, or UIs.
• Scalability: Layers and modules can evolve independently.

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3️⃣ Analogy

Think of a house:

• Foundation/Core (Entities): Strong, stable, never changes.
• Rooms/Use Cases: Define the purpose of each space.
• Exterior/Infrastructure: Walls, doors, windows → can change without touching the foundation.
• Furniture/UI: Can be replaced without affecting the structure.

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