Hexagonal Architecture (A.K.A Ports & Adapters) Cherif BOUCHELAGHEM 

What is architecture? 

What is architecture? “Is the art of drawing lines” Robert C. Martin (Uncle Bob) 

What is architecture? Those lines generally represent boundaries 

What is hexagonal architecture? 

Hexagonal Architecture: What is it? “Create your application to work without either a UI or a database so you can run automated regression-tests against the application, work when the database becomes unavailable, and link applications together without any user involvement.” Alistair Cockburn: Hexagonal architecture 

The web is delivery mechanism 

The delivery mechanism is detail 

Database is detail 

Hexagonal Architecture: What is it? Drawing from the the original article. Each facet of the hexagon represents a port (a technology-independent protocol capturing a reason for a discussion) 

Hexagonal Architecture: What is it? Ports, are abstractions on the boundaries. Adapters, are implementations of the given ports. 

Hexagonal Architecture: What is it? - Ports: Are abstraction defined by the application - Adapters: are the implementation of the ports (abstraction) that connect the application with the outside world. The outside world is anything that is not really important to solve the problem we trying to solve: Database, UI (Delivery mechanism), frameworks (Mobile, web, … etc) 

Hexagonal Architecture: What is it? We can have more than just 6 facets of the hexagon 

About unit tests A test is not a unit test if: - It talks to a database - It communicates across the network - It touches the file system - You have to do things to your environment to run it (eg, change config files, comment line) - Tests that do this are integration tests. 

Hexagonal Architecture: What is it? 

Why? 

Hexagonal architecture: Why? Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from its eventual run-time devices and databases. 

About unit tests 

About unit tests For isolation usually people talk about mocks, in reality mocks are one of the test doubles that help to run make unit tests: - Mock - Fake - Spy - Stub - Dummy 

The problem to solve in this workshop 

Calculate product taxes - Product has a category - Every category of products has its own tax rate (.17) - The tax calculation is based on simple formula: Product base cost + (product base cost * category tax rate) Source Code