Clean Architecture in .NET: Practical Implementation

Clean Architecture is more than just a buzzword—it’s a blueprint for building systems that are independent of frameworks, UI, databases, and infrastructure concerns. Coined by Uncle Bob (Robert C. Martin), it emphasizes separation of concerns, dependency inversion, and maintainability.

In this guide, we’ll walk through how to implement Clean Architecture in a real .NET application with proper project structure, code organization, and dependency flow.

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🧱 What Is Clean Architecture?

At its core, Clean Architecture divides your system into concentric layers with clear boundaries. The main rule is:

Dependencies can only point inward.

🌀 Layers Overview

1. Domain Layer: Contains core business logic, entities, value objects

2. Application Layer: Use cases, interfaces, DTOs

3. Infrastructure Layer: DB access, third-party integrations, file systems

4. Presentation Layer: API controllers, web UI, gRPC endpoints, etc.

Each layer should depend only on the layers inward from it. For example, Infrastructure knows about Application, but Application does not know about Infrastructure.

🧩 Related Architectural Styles

Clean Architecture shares core principles with other popular patterns like:

• Hexagonal Architecture (Ports and Adapters): Focuses on decoupling application core from external concerns through ports (interfaces) and adapters (implementations). This emphasizes testability and interchangeability of external systems.

• Onion Architecture: Similar concentric layout with a strong emphasis on Domain Models at the core, surrounded by Application and Infrastructure layers. It avoids data access or UI dependencies from leaking into business logic.

These styles all encourage:

• Strong separation of concerns

• Inversion of dependencies

• Testability and maintainability

You can adopt ideas from all three as long as you respect the core principle: keep your business logic independent from frameworks and infrastructure.

At its core, Clean Architecture divides your system into concentric layers with clear boundaries. The main rule is:

Dependencies can only point inward.

🌀 Layers Overview

1. Domain Layer: Contains core business logic, entities, value objects

2. Application Layer: Use cases, interfaces, DTOs

3. Infrastructure Layer: DB access, third-party integrations, file systems

4. Presentation Layer: API controllers, web UI, gRPC endpoints, etc.

Each layer should depend only on the layers inward from it. For example, Infrastructure knows about Application, but Application does not know about Infrastructure.

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📂 Project Structure in .NET

A typical folder layout:

/src
  /Domain
    - Entities
    - ValueObjects
    - Interfaces (e.g., IAggregateRoot)

  /Application
    - Interfaces (IEmailService, IRepository<T>)
    - DTOs
    - UseCases (Commands, Queries, Handlers)

  /Infrastructure
    - EF Core DbContext
    - Implementations of IRepository
    - External service clients

  /WebAPI
    - Controllers
    - Middlewares
    - Dependency injection wiring
/tests
  /UnitTests
  /IntegrationTests

You can also split into separate projects if needed:

• Project.Domain

• Project.Application

• Project.Infrastructure

• Project.WebAPI

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🔁 Dependency Flow and Inversion

Traditional layered architectures often have:

UI → Business Logic → Data Access

In Clean Architecture, it becomes:

Infrastructure ← Application ← Domain
           ↑         ↑
        Web/API ←

This inversion is enabled via interfaces and dependency injection.

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🛠️ Key Practices

1. Define Entities in the Domain Layer

public class Order : IAggregateRoot
{
    public Guid Id { get; private set; }
    public List<OrderItem> Items { get; private set; }

    public void AddItem(Product product, int quantity) { ... }
}

2. Define Use Cases in the Application Layer

public class CreateOrderCommand : IRequest<Guid>
{
    public Guid CustomerId { get; set; }
    public List<OrderItemDto> Items { get; set; }
}

public class CreateOrderHandler : IRequestHandler<CreateOrderCommand, Guid>
{
    private readonly IOrderRepository _repo;
    private readonly IUnitOfWork _uow;

    public async Task<Guid> Handle(CreateOrderCommand request, CancellationToken ct)
    {
        var order = new Order(...);
        _repo.Add(order);
        await _uow.CommitAsync();
        return order.Id;
    }
}

3. Infrastructure Implements Contracts

public class EfOrderRepository : IOrderRepository
{
    private readonly AppDbContext _ctx;

    public void Add(Order order) => _ctx.Orders.Add(order);
    public async Task<Order> GetByIdAsync(Guid id) => await _ctx.Orders.FindAsync(id);
}

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⚙️ Technologies That Fit Well

• MediatR for use case orchestration (Application Layer)

• FluentValidation for validation logic

• AutoMapper to convert between DTOs and domain models

• Entity Framework Core for persistence

• Serilog / OpenTelemetry for logging & tracing

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✅ Advantages of Clean Architecture

• Easy to test (business logic has no external dependencies)

• Maintainable and loosely coupled

• Technology-agnostic

• Encourages good design habits

• Supports team scaling and onboarding

⚠️ Challenges and Trade-offs

• Initial Complexity: Requires more upfront planning and structure

• Learning Curve: Developers unfamiliar with separation of layers or dependency inversion may struggle at first

• Potential Over-Engineering: In small or short-lived projects, this structure may feel heavy

• More Boilerplate: Interfaces, DTOs, and mapping logic can add overhead

While Clean Architecture offers great long-term value, teams should assess whether its structure aligns with the project’s scale and lifespan.

🧠 Final Thoughts

Clean Architecture offers a robust way to structure software systems that prioritize independence, testability, and long-term maintainability. The approach is especially powerful in complex applications—but it does come with trade-offs.

If you're working in a greenfield project or aiming for clean separation of concerns, it's a strong fit. However, if you're dealing with very simple use cases or small teams, you might prefer a lightweight architecture with similar principles but less overhead.

Start small. Let your domain shape your architecture. Iterate as your app grows.

In the next article, we’ll dive into CQRS with MediatR, a common pattern used in Clean Architecture for separating commands and queries.

Happy architecting! 🧱