When building enterprise-grade backend APIs, separating business logic from infrastructure concerns is crucial for long-term testability and maintainability.

1. The Core Layers of Clean Architecture

Clean Architecture enforces a strict inward dependency rule where domain rules remain completely agnostic of databases, UI frameworks, or third-party web services:

  • Domain: Enterprise business entities, value objects, domain events, and enums.
  • Application: Command and Query handlers (CQRS), business validation with FluentValidation, and DTO mappings.
  • Infrastructure: Entity Framework Core database contexts, migrations, SMTP mailing, and external REST clients.
  • Web API: RESTful controllers, rate limiters, JWT authentication middleware, and Swagger/OpenAPI documentation.

2. Implementing CQRS with MediatR

By separating read queries (optimized for speed) from write commands (enforcing business constraints), MediatR eliminates bloated controller classes and isolates single-responsibility handlers.