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.

Get Your Hands Dirty on Clean Architecture by Tom Hombergs.png

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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

# Validation

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 with a business rule?

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, like we did with the `@NotNull` annotations previously, while a business rule needs more context.

# Syntactical vs semantical

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 if the source and target accounts exist.

In contrast, the rule "the transfer amount must be greater than zero" can be validated without access to the model and thus can be implemented as part of the input validation.



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

Validating Business Rules

Validation