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About the Book

Most .NET teams start with a classic three-layer architecture — and most eventually hit the same wall. The business logic quietly becomes entangled with Entity Framework, the API controllers reach deep into domain classes, and swapping a database or adding a test suite turns into a rewrite.

Clean Architecture with Onion Principles, DDD, Facade Layer and CQS offers a way out. This guide presents a four-layer architecture that puts your business domain at the center, shields it with an explicit Facade contract, and splits every Use Case into a Command or a Query — giving you a codebase that is testable, flexible, and ready to evolve.

What You'll Learn

The book walks through the complete architecture layer by layer, with working C# code at every step. You'll see how to model entities with private setters and explicit methods so that business rules can never be bypassed. You'll learn why a dedicated Facade layer — containing only interfaces and DTOs — solves the coupling problems that plague most Clean Architecture implementations. And you'll discover how Command Query Separation at the Use Case level naturally prepares your system for CQRS without requiring it from day one.

Concrete topics include DDD entity design with Value Objects and Domain Services, structuring Use Cases as single-responsibility Command and Query classes, defining a Facade contract that decouples every external consumer from the core, implementing repositories and query handlers in the Infrastructure layer with Entity Framework Core, enforcing the Dependency Rule through .NET project references, and unit-testing each layer in isolation using Moq.

Who This Book Is For

This book is for .NET developers and architects who build line-of-business applications and want a proven structure that scales beyond simple CRUD. Whether you are starting a greenfield project or refactoring an existing monolith, the patterns here give you a clear path forward. Familiarity with C# and ASP.NET Core is assumed; prior knowledge of DDD or Clean Architecture is helpful but not required.

About the Author

Kaj Bromose is a software architect specializing in .NET enterprise applications. His work focuses on bridging the gap between architectural theory and day-to-day development practice.

ORCID: 0000-0002-8974-2718

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