Clean Architecture in ASP.NET Core

Introduction

Clean Architecture (Uncle Bob) organizes ShopNest enterprise apps so business rules never depend on EF Core, UI, or email — only the reverse. Dependencies point inward toward the Domain.

After this article you will

• Map Domain, Application, Infrastructure, Presentation layers
• Apply the Dependency Rule with project references
• Place entities, use cases, and EF in correct layers
• Wire DI across layer boundaries
• Compare Clean Architecture to traditional N-tier

Prerequisites

• Article 43 — SignalR — Real-Time Web Applications
• ShopNest API, EF Core, and DI from prior modules

Concept deep-dive

┌─────────────────────────────────────┐
│  Presentation (Web API, MVC)        │
├─────────────────────────────────────┤
│  Infrastructure (EF, Email, Files)    │
├─────────────────────────────────────┤
│  Application (Use cases, DTOs, Val)   │
├─────────────────────────────────────┤
│  Domain (Entities, Events, Interfaces)│  ← no outward deps
└─────────────────────────────────────┘

Domain: Task, Project entities; ITaskRepository interface.
Application: CreateTaskCommand, handlers, validators.
Infrastructure: TaskRepository, ShopNestDbContext implements interfaces.
Presentation: TasksController calls MediatR or application services.

// Domain — zero NuGet except maybe abstractions
public interface ITaskRepository
{
    Task<TaskItem?> GetByIdAsync(Guid id, CancellationToken ct);
    Task AddAsync(TaskItem task, CancellationToken ct);
}

// Infrastructure references Domain + Application
public class EfTaskRepository : ITaskRepository { ... }

Project references: Web → Application → Domain; Infrastructure → Application + Domain. Web must NOT reference Infrastructure types in controllers — only register via DI extension.

Hands-on — ShopNest Enterprise Task Management System

1. Solution: ShopNest.Domain, .Application, .Infrastructure, .Web.
2. CreateTask use case in Application; EF repo in Infrastructure.
3. AddInfrastructure(this IServiceCollection) extension in Web Program.cs.
4. Verify Domain project has no reference to EF or ASP.NET.

Common errors & best practices

• DbContext in Domain — violates dependency rule.
• Controllers calling _context directly — skip Application layer.
• Over-engineering simple CRUD — Clean Architecture pays off on complex domains.

Interview questions

Q: Dependency Rule?
A: Source code dependencies only point inward — outer layers implement inner interfaces.

Q: Clean vs N-tier?
A: N-tier is technical layers; Clean is business-centric with domain at center.

Q: Where do DTOs live?
A: Application layer (use case input/output), not Domain.

Summary

• Domain has no framework dependencies
• Application orchestrates use cases
• Infrastructure is pluggable via interfaces
• ShopNest task management scales with team boundaries

Previous: SignalR — Real-Time Web Applications
Next: CQRS Pattern with MediatR

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