Clean Architecture for ASP.NET Core Projects: A Layered Approach

Understanding Clean Architecture Principles

Clean Architecture, popularized by Robert C. Martin (Uncle Bob), advocates for organizing code around business logic, keeping it independent of external concerns such as UI, databases, and frameworks. The core goal is to create systems that are easier to test, maintain, and evolve over time by establishing clear boundaries and dependency rules. This approach fundamentally shifts dependencies inward, meaning outer layers depend on inner layers, but inner layers remain oblivious to outer ones.

The Four-Layer Project Structure

A common and effective way to implement Clean Architecture in ASP.NET Core involves splitting the solution into four distinct projects, each with a specific responsibility:

• MyProject.Domain: Contains core business rules, entities, value objects, enums, and custom exceptions. It has zero external dependencies.
• MyProject.Application: Defines application-specific business rules and use cases. It orchestrates domain entities and defines interfaces for external dependencies (e.g., repositories, services).
• MyProject.Infrastructure: Provides concrete implementations for interfaces defined in the Application layer, handling external concerns like database access, external APIs, and file storage.
• MyProject.API: The entry point of the system, typically an ASP.NET Core web API, which handles requests, maps them to application commands/queries, and wires up dependency injection for the concrete implementations from the Infrastructure layer.

Dependency Direction: The Most Important Rule

The hierarchical dependency flow is critical to Clean Architecture. The innermost layer (Domain) has no dependencies, while outer layers depend on inner ones. Specifically, the API layer depends on the Application layer, which in turn depends on the Domain layer. Crucially, the Infrastructure layer also depends on the Application layer (e.g., implementing interfaces defined in Application), preventing the Application or Domain layers from being coupled to specific infrastructure choices.

API
 ↓
Application
 ↓
Domain

Infrastructure → Application