Single Responsibility Principle (SRP) in context of Clean Architecture

The Single Responsibility Principle (SRP) is one of the SOLID principles of object-oriented design, and it emphasizes that a class or module should have only one reason to change. In the context of Clean Architecture, SRP becomes crucial for maintaining a system that is easy to understand, modify, and extend. Clean Architecture promotes a separation of concerns, and SRP aligns well with this goal.

Here's how SRP can be applied within the context of Clean Architecture:

1. Separation of Concerns:

   • Each class or module in Clean Architecture should have a clear and distinct responsibility. For example, a class should either handle business logic, interact with the database, or deal with the user interface, but not all of these responsibilities.

2. Isolation of Business Rules:

   • Business rules and logic should be isolated in high-level policy modules (application layer) such as use cases or interactors. These modules should focus on the core business logic and be independent of external details.

3. Adherence to Single Responsibility:

   • Each class or module should have a single responsibility and reason to change. For example, a class responsible for handling user authentication should not also be responsible for database access or UI rendering.

4. Separate I/O from Business Logic:

   • Keep input/output (I/O) mechanisms, such as database access, web frameworks, and UI components, separate from the core business logic. This allows the business logic to remain independent and makes it easier to adapt the system to different I/O mechanisms.

5. Clear Abstractions:

   • Use abstractions and interfaces to clearly define the responsibilities of classes and modules. This allows for flexibility in changing implementations without affecting the overall system.

Here's a simplified example in C# within the context of Clean Architecture:

// High-level policy module (Application Layer)
public class OrderService
{
    private readonly IOrderRepository _orderRepository;

    public OrderService(IOrderRepository orderRepository)
    {
        _orderRepository = orderRepository;
    }

    public void PlaceOrder(Order order)
    {
        // Business logic for placing an order...
        _orderRepository.SaveOrder(order);
    }

    // Other business methods...
}

// Interface for low-level detail module
public interface IOrderRepository
{
    void SaveOrder(Order order);
    // Other data access methods...
}

// Low-level detail module (Database Access)
public class OrderRepository : IOrderRepository
{
    public void SaveOrder(Order order)
    {
        // Database access logic to save the order...
    }

    // Other data access methods...
}

In this example, the OrderService class in the application layer has a single responsibility, which is to handle the business logic related to orders. The OrderRepository class in the infrastructure layer is responsible for database access and implements the IOrderRepository interface.

By adhering to the Single Responsibility Principle within Clean Architecture, you create a system where each class or module has a clear and focused responsibility, making the codebase more maintainable and adaptable to change.