Discover Hexagonal Architecture to create web applications with isolated, testable layers. Gain insights into designing clean, maintainable modules and advocating for suitable techniques for your application.

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This course will teach you all about creating a web application in the Hexagonal Architecture style. Hexagonal Architecture promotes the separation of concerns by encapsulating logic in different layers of the application. This enables a higher level of isolation, testability, and control over your business specific code. 

You will learn how to design software modules and complete applications in a clean and maintainable manner, while also learning how to advocate for a certain technique given your application and constraints.

By the end of this course, you will have a greater understanding of how to implement software architecture, a key skill for any senior developer.

Hexagonal Software Architecture for Web Applications

# Dependency in layered architecture

In our layered architecture, the cross-layer dependencies always point downward to the next layer. When we apply the Single Responsibility Principle 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 to 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! 

# How can we get rid of this dependency? 

The Dependency Inversion Principle provides the answer.

In contrast to the #key# SRP: Single Responsibility Principle #key#, the #key# DIP: Dependency Inversion Principle #key# means what the name suggests:

> *We can turn around (invert) the direction of any dependency within our codebase*[$^3$](https://www.educative.io/courses/hexagonal-architecture-web-apps/appendix-i#any-dependency).

Actually, we can only invert dependencies when we have control over the code on both sides of the dependency. If we have a dependency to a third-party library, we cannot invert it as we don't control the code of that library.

# How does it work?


Learn about the dependency inversion principle and how it can help you develop clean software architecture.

Before We Begin

What's Wrong with Layers?

Inverting Dependencies

Organizing Code

Implementing a Use Case

Implementing a Web Adapter

Implementing a Persistence Adapter

Testing Architecture Elements

Mapping Between Boundaries

Assembling the Application

Enforcing Architecture Boundaries

Taking Shortcuts Consciously

Assessment

Conclusion

Appendix

The Dependency Inversion Principle

Dependency in layered architecture