Layered Architecture in ASP.NET Core: Simple, Structured, and Still Relevant (Part 2)

In the first part of this series, we explored why software architecture matters—especially in .NET projects that grow beyond simple CRUD applications.

Today, we’re starting with one of the most familiar patterns: Layered Architecture. It’s often the first structured approach developers learn—and with good reason. It brings clarity and separation of concerns without much overhead.

Let’s break it down.

What Is Layered Architecture?

Layered Architecture, also known as n-tier architecture, separates your application into logical layers where each layer has a specific responsibility.

A typical ASP.NET Core project using this pattern includes:

Presentation Layer (e.g., Controllers, Razor Pages, APIs)

Application Layer (e.g., Services, Business Logic)

Data Access Layer (e.g., Repositories, EF Core)

Domain Layer (optional, for core models and logic)

+-----------------------+
|   Presentation Layer  |
|  (Controllers / API)  |
+-----------------------+
           ↓
+-----------------------+
|   Application Layer   |
| (Services / Use Cases)|
+-----------------------+
           ↓
+-----------------------+
|   Data Access Layer   |
|   (EF Core / DB Code) |
+-----------------------+

Each layer only talks to the layer directly below it.

Why Use Layered Architecture?

✅ Separation of concerns
✅ Improves maintainability
✅ Simplifies testing (especially service logic)
✅ Well-supported in tutorials, teams, and tooling

It helps you avoid the "God Controller" or "fat service" problems by pushing logic to the right place.

Common Mistakes

Despite its simplicity, developers often misuse this pattern:

❌ Skipping the application layer, putting logic in controllers

❌ Services that just forward calls to the database

❌ Tight coupling between layers

❌ Ignoring validation and business rules

🛠️ A Simple Example in ASP.NET Core

Let’s say we’re building a basic order system.

1 Domain Models

public class Order
{
    public Guid Id { get; set; }
    public DateTime CreatedAt { get; set; }
    public decimal TotalAmount { get; set; }
}

2 Application Layer

 public interface IOrderService
{
    Task<Guid> CreateOrderAsync(OrderDto dto);
}

public class OrderService : IOrderService
{
    private readonly IOrderRepository _repository;

    public OrderService(IOrderRepository repository)
    {
        _repository = repository;
    }

    public async Task<Guid> CreateOrderAsync(OrderDto dto)
    {
        var order = new Order
        {
            Id = Guid.NewGuid(),
            CreatedAt = DateTime.UtcNow,
            TotalAmount = dto.Total
        };

        await _repository.AddAsync(order);
        return order.Id;
    }
}

3 Data Access Layer

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

public class OrderRepository : IOrderRepository
{
    private readonly AppDbContext _context;

    public OrderRepository(AppDbContext context)
    {
        _context = context;
    }

    public async Task AddAsync(Order order)
    {
        _context.Orders.Add(order);
        await _context.SaveChangesAsync();
    }
}

4 Presentation Layer (Controller)

[ApiController]
[Route("api/[controller]")]
public class OrdersController : ControllerBase
{
    private readonly IOrderService _orderService;

    public OrdersController(IOrderService orderService)
    {
        _orderService = orderService;
    }

    [HttpPost]
    public async Task<IActionResult> CreateOrder([FromBody] OrderDto dto)
    {
        var id = await _orderService.CreateOrderAsync(dto);
        return Ok(id);
    }
}

Folder Structure

/MyApp
  /Controllers
    OrdersController.cs
  /Services
    IOrderService.cs
    OrderService.cs
  /Repositories
    IOrderRepository.cs
    OrderRepository.cs
  /Models
    Order.cs
    OrderDto.cs

Is Layered Architecture Still Relevant?

Yes—but with nuance.

For small to medium apps, it works great. For complex domains or large teams, it may need enhancements like:

• CQRS

• MediatR

• Onion/Clean Architecture

The key is understanding when it’s enough—and when you need to evolve.

When to Use This Pattern

✅ MVPs or startup products
✅ Internal tools
✅ Projects where complexity is moderate
✅ Teams new to architecture patterns

Up Next

In Part 3, we’ll level up to Onion Architecture—a more flexible structure where dependencies flow inward, not outward.

If Layered Architecture is your first step into designing clean code, Onion Architecture is the next.

Wrap-Up

Layered Architecture is often underestimated, but when done right, it's clean, simple, and effective. It gives your team a structure without overengineering.

Thanks for following along!

Like, comment, or follow for Part 3 coming soon.
Have questions or use this in production? Let’s discuss in the comments!