Architecture Patterns

Apply Clean Architecture, Hexagonal Architecture, and Domain-Driven Design to build maintainable, testable, and scalable backend systems.

Core Concepts

Clean Architecture (Uncle Bob)

Layers (dependency flows inward):

• •Entities: Core business models
• •Use Cases: Application business rules
• •Interface Adapters: Controllers, presenters, gateways
• •Frameworks & Drivers: UI, database, external services

Principles: Dependencies point inward. Inner layers know nothing about outer layers. Business logic independent of frameworks.

Hexagonal Architecture (Ports and Adapters)

Components:

• •Domain Core: Business logic
• •Ports: Interfaces defining interactions
• •Adapters: Implementations (database, REST, message queue)

Benefits: Swap implementations easily, technology-agnostic core, clear separation of concerns.

Domain-Driven Design (DDD)

Strategic Patterns:

• •Bounded Contexts: Separate models for different domains
• •Context Mapping: How contexts relate
• •Ubiquitous Language: Shared terminology

Tactical Patterns:

• •Entities: Objects with identity
• •Value Objects: Immutable objects defined by attributes
• •Aggregates: Consistency boundaries
• •Repositories: Data access abstraction
• •Domain Events: Things that happened

Implementation Examples

Load the appropriate example file based on the pattern being implemented:

• •Clean Architecture: See examples/clean-architecture-example.md for complete layered implementation with entities, use cases, repositories, and controllers
• •Hexagonal Architecture: See examples/hexagonal-example.md for ports and adapters with production and test implementations
• •DDD Tactical Patterns: See examples/ddd-example.md for value objects, entities, aggregates, and domain events

Best Practices

1. •Dependency Rule: Dependencies always point inward
2. •Interface Segregation: Small, focused interfaces
3. •Business Logic in Domain: Keep frameworks out of core
4. •Test Independence: Core testable without infrastructure
5. •Bounded Contexts: Clear domain boundaries
6. •Ubiquitous Language: Consistent terminology
7. •Thin Controllers: Delegate to use cases
8. •Rich Domain Models: Behavior with data

Common Pitfalls

• •Anemic Domain: Entities with only data, no behavior
• •Framework Coupling: Business logic depends on frameworks
• •Fat Controllers: Business logic in controllers
• •Repository Leakage: Exposing ORM objects
• •Missing Abstractions: Concrete dependencies in core
• •Over-Engineering: Clean architecture for simple CRUD