Onion Architecture

As applications grow larger and more complex, there arises a need for better ways to manage dependencies and ensure that different parts of the system remain loosely coupled.

Onion Architecture is one such approach, designed to promote separation of concerns, maintainability, and flexibility.

At its core, Onion Architecture organizes the application into concentric layers. The innermost layer contains the business rules and domain logic, while the outer layers handle more peripheral concerns, such as data access or user interfaces.

The principle behind this architecture is that dependencies point inward—the inner layers have no knowledge of the outer layers.

Key Features of Onion Architecture

1. Separation of concerns: each layer in the architecture is responsible for a specific type of logic, helping maintain clear boundaries between components;
2. Dependency inversion: outer layers depend on the inner layers (never the other way around). For example, the infrastructure layer depends on the core logic but the core layer remains unaware of the outer systems;
3. Maintainability: changes in technology (e.g., switching from one database to another) only impact the outer layers, keeping the business logic unaffected;
4. Flexibility and scalability: onion Architecture allows for growth without compromising the core logic since you can add or modify outer layers as needed.

Pros and Cons

In an e-commerce system designed with Onion Architecture, the platform is structured into distinct layers, each serving a specialized purpose while ensuring that the core business logic remains unaffected by external factors:

• Domain layer (core business logic): this is the heart of the system, containing rules for processing orders, managing products, and handling payments; it focuses solely on business logic without knowledge of databases, UI, or external services;
• Application layer: this layer coordinates actions between the domain and external services; for example, it manages workflows like validating orders and processing payments; it orchestrates actions but does not contain detailed business rules;
• Presentation layer (UI): this is the interface customers interact with, such as a web page or mobile app; it allows users to browse products and place orders, sending requests to the application layer to trigger business logic;
• Infrastructure layer (persistence, APIs, etc.): this outer layer handles technical details like databases and payment gateways; it allows for changes (e.g., switching payment providers) without affecting core business logic.