Onion Architecture

Introduction

Onion Architecture is a software architectural pattern that aims to address the common problems associated with traditional layered architectures. It emphasizes the separation of concerns, promoting maintainability and testability of applications.

Key Concepts

• Separation of concerns
• Dependency inversion
• Testability
• Flexibility

Layers of Onion Architecture

The Onion Architecture consists of several concentric layers:

1. Core Layer: Contains the business logic and domain entities.
2. Domain Services Layer: Contains business rules and application services.
3. Application Layer: Handles application logic, orchestration, and communication between layers.
4. Infrastructure Layer: Contains data access, external services, and other infrastructure concerns.

Implementation

Here is a basic structure of an Onion Architecture implementation in C#:

namespace MyApplication.Core.Entities
{
    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

namespace MyApplication.Domain.Services
{
    public interface IUserService
    {
        User GetUser(int id);
    }

    public class UserService : IUserService
    {
        public User GetUser(int id)
        {
            // Logic to retrieve user
        }
    }
}

namespace MyApplication.Application
{
    public class UserController
    {
        private readonly IUserService _userService;

        public UserController(IUserService userService)
        {
            _userService = userService;
        }

        public User GetUser(int id)
        {
            return _userService.GetUser(id);
        }
    }
}
                

Best Practices

• Keep the core layer independent from other layers.
• Use interfaces for dependencies to enable testing.
• Maintain a clear separation of concerns between layers.
• Implement dependency injection to manage dependencies.

FAQ