Clean Architecture is not merely a folder convention. Its purpose is to protect business rules from volatile details such as databases, web frameworks, and third-party services. In long-lived applications this separation improves testability, reduces the cost of technology changes, and gives teams a shared model for deciding where code belongs.

Understanding the dependency rule

Domain sits at the center and depends on no outer project. Application defines use cases and the interfaces they require. Infrastructure implements those interfaces with SQL Server, email, storage, or other technologies. Web translates HTTP requests into use-case calls. References point inward, so Domain never needs to understand Entity Framework or MVC.

Creating an order use case

The Application layer in this example has no knowledge of database mechanics. It only consumes the contract it needs, while Infrastructure can provide an EF Core implementation later.

public interface IOrderRepository
{
    Task AddAsync(Order order, CancellationToken ct);
}

public sealed class CreateOrderHandler
{
    private readonly IOrderRepository _orders;

    public CreateOrderHandler(IOrderRepository orders) => _orders = orders;

    public async Task<int> Handle(CreateOrder command, CancellationToken ct)
    {
        var order = Order.Create(command.CustomerId, command.Items);
        await _orders.AddAsync(order, ct);
        return order.Id;
    }
}

The handler focuses on business flow. SQL, HTTP clients, and file logging do not leak into the class. Tests can supply a fake repository, while production dependency injection binds the same interface to EF Core. The order rules can therefore be verified without starting a real database.

Implementation steps

1. Define entities, value objects, and business invariants in Domain without adding framework packages.
2. Place use cases, DTOs, and outbound interfaces in Application.
3. Implement DbContext, repositories, and service adapters in Infrastructure.
4. Keep Web responsible for validation, authentication, routing, and HTTP responses.
5. Test successful flows as well as validation failures and boundary conditions for each use case.

Common mistakes

• Creating a generic repository for every table and rebuilding capabilities already supplied by EF Core.
• Using DbContext, IConfiguration, or HttpContext inside Domain and reversing the intended dependency direction.
• Treating the number of layers as a goal and adding unnecessary abstractions to a genuinely small application.

Conclusion

When applied with discipline, Clean Architecture keeps business behavior—not technology—at the center of the codebase. The initial structure may look expensive for a tiny CRUD service, but its value becomes clear when data sources change, test coverage grows, and multiple teams contribute. A practical adoption path is to complete one important use case with these rules before expanding the pattern.