Onion Architecture Vs Hexagonal Architecture
The Onion Architecture and the Hexagonal Architecture (also known as Ports and Adapters or Ports and Adapters Architecture) share some similarities in their core principles, aiming to create maintainable, testable, and loosely coupled software systems. However, they have differences in their structural layout and focus
Here are the key distinctions between the two:
1: Structural Layout:
Onion Architecture: It is structured in concentric circles or layers, with the core domain at the center, surrounded by layers of increasing abstraction. The innermost layer contains the core domain logic and entities, with each outer layer representing additional levels of abstraction and dependencies.
Hexagonal Architecture: Hexagonal Architecture focuses on dividing the application into layers based on functionality rather than layers of abstraction. It comprises an inner core surrounded by a layer of ports (interfaces) and an outer layer of adapters. The core represents the business logic, ports define the interfaces for interacting with the core, and adapters implement those interfaces to interact with external systems or frameworks.
2: Dependency Direction:
Onion Architecture: The dependencies flow inward. The core domain layer remains independent of external concerns, and dependencies are directed towards the center. Inner layers encapsulate business logic, and outer layers contain infrastructure or framework-related concerns.
Hexagonal Architecture: The core (business logic) is isolated and unaware of the external systems. It defines ports (interfaces) that represent the application’s capabilities without specifying how they will be implemented. Adapters, located in the outer layer, implement these ports, enabling interaction with external systems or frameworks.
3: Focus:
Onion Architecture: Emphasizes the separation of concerns by organizing code into layers. It aims to create a clear distinction between the core domain and infrastructure concerns while ensuring that the core remains independent and agnostic of the outer layers.
Hexagonal Architecture: Focuses on defining clear boundaries between the application core and its external dependencies. It promotes the concept of ports and adapters, allowing the application to be easily integrated with different external systems by swapping adapters while keeping the core unchanged.
