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)

The Dependency Inversion Principle

In our layered architecture, the cross-layer dependencies always point downward, to the next layer. When we apply the SRP on a high level, we notice that the upper layers have more reasons to change than the lower layers.

Thus, due to the domain layer's dependency on the persistence layer, each change in the persistence layer potentially requires a change in the domain layer. But the domain code is the most important code in our application. We don't want to have to change it when something changes in the persistence code.

So, how can we get rid of this dependency?

The Dependency Inversion Principle (DIP) provides the answer.

In contrast to the SRP, the DIP means what the name suggests:

We can turn around (invert) the direction of any dependency within our codebase.

Actually, we can only invert dependencies when we have control over the code on both sides of the dependency. If we have a dependency on a third-party library, we cannot invert it, since...