Book Image

Get Your Hands Dirty on Clean Architecture

By : Tom Hombergs
Book Image

Get Your Hands Dirty on Clean Architecture

By: Tom Hombergs

Overview of this book

Building for maintainability is key to keeping development costs low and processes easy. The second edition of Get Your Hands Dirty on Clean Architecture is here to equip you with the essential skills and knowledge to build maintainable software. With this comprehensive guide, you’ll explore the drawbacks of conventional layered architecture and the advantages of domain-centric styles such as Robert C. Martin's Clean Architecture and Alistair Cockburn's Hexagonal Architecture. Then, you’ll dive into hands-on explanations on how to convert hexagonal architecture into actual code. You'll learn in detail about different mapping strategies between the layers of hexagonal architecture and discover how to assemble the architectural elements into an application. Additionally, you’ll understand how to enforce architecture boundaries, which shortcuts produce what types of technical debt, and how, sometimes, it is a good idea to willingly take on those debts. By the end of this second edition, you'll be armed with a deep understanding of the hexagonal architecture style and be ready to create maintainable web applications that save money and time.
Table of Contents (13 chapters)

Validating Business Rules

While validating input is not part of the use case logic, validating business rules definitely is. Business rules are the core of the application and should be handled with appropriate care. But when are we dealing with input validation and when are we dealing with business rule validation?

A very pragmatic distinction between the two is that validating a business rule requires access to the current state of the domain model while validating input does not. Input validation can be implemented declaratively, as we did with the @NotNull annotations, while a business rule needs more context.

We might also say that input validation is a syntactical validation, while a business rule is a semantical validation in the context of a use case.

Let's take the rule "the source account must not be overdrawn." By the definition above, this is a business rule since it needs access to the current state of the model to check whether the source and target accounts do...