Clean Architecture

Robert C. Martin

a.k.a. Uncle Bob

Business Rules are the most important part of an application

Stuff we want to keep
Stuff we want to test
Stuff we want to hide

So, everything else is plugins

Database
UI
Web
Services

By coincidence (or not)

DB is hard to test
UI is hard to test
Web is hard to test
External services are hard to test

The Clean Architecture

Inversion of Control

"Don't call us, we'll call you"

High-level modules should not depend on low-level modules. Both should depend on abstractions.
Abstractions should not depend on details. Details should depend on abstractions.

Entities

"Entities encapsulate Enterprise wide business rules"
They are the least likely to change when something external changes

Use Cases

It encapsulates and implements all of the use cases of the system
Orchestrate the flow of data to and from the entities
What your application does

Interface Adapters

"Converts data from the format most convenient for the use cases and entities, to the format most convenient for some external agency"

SQL queries
MVC
ORM

External world

Details
MySQL
Web Server

Cool consequences

It's fairly easy to tell what your application does
Test your business rules without external dependencies
Postpone decision making

➜ tree -L 1
.
├── assets
├── channels
├── controllers
├── helpers
├── jobs
├── mailers
├── models
└── views

8 directories, 0 files

➜ tree -L 2
.
├── assets
│   ├── config
│   ├── images
│   ├── javascripts
│   └── stylesheets
├── channels
│   └── application_cable
├── controllers
│   ├── application_controller.rb
│   ├── concerns
│   ├── todo_items_controller.rb
│   └── todo_lists_controller.rb
├── helpers
│   ├── application_helper.rb
│   ├── todo_items_helper.rb
│   └── todo_lists_helper.rb
├── jobs
│   └── application_job.rb
├── mailers
│   └── application_mailer.rb
├── models
│   ├── application_record.rb
│   ├── concerns
│   ├── todo_item.rb
│   └── todo_list.rb
└── views
    ├── layouts
    ├── todo_items
    └── todo_lists

18 directories, 11 files

➜ tree -L 3
.
├── assets
│   ├── config
│   │   └── manifest.js
│   ├── images
│   ├── javascripts
│   │   ├── application.js
│   │   ├── cable.js
│   │   ├── channels
│   │   ├── todo_items.coffee
│   │   └── todo_lists.coffee
│   └── stylesheets
│       ├── application.scss
│       ├── scaffolds.scss
│       ├── todo_items.scss
│       └── todo_lists.scss
├── channels
│   └── application_cable
│       ├── channel.rb
│       └── connection.rb
├── controllers
│   ├── application_controller.rb
│   ├── concerns
│   ├── todo_items_controller.rb
│   └── todo_lists_controller.rb
├── helpers
│   ├── application_helper.rb
│   ├── todo_items_helper.rb
│   └── todo_lists_helper.rb

├── jobs
│   └── application_job.rb
├── mailers
│   └── application_mailer.rb
├── models
│   ├── application_record.rb
│   ├── concerns
│   ├── todo_item.rb
│   └── todo_list.rb
└── views
    ├── layouts
    │   ├── application.html.erb
    │   ├── mailer.html.erb
    │   └── mailer.text.erb
    ├── todo_items
    │   ├── _form.html.erb
    │   └── _todo_item.html.erb
    └── todo_lists
        ├── _form.html.erb
        ├── _todo_list.json.jbuilder
        ├── edit.html.erb
        ├── index.html.erb
        ├── index.json.jbuilder
        ├── new.html.erb
        ├── show.html.erb
        └── show.json.jbuilder

19 directories, 35 files

...a simple example

Final Considerations

It's not something completely new and innovative:
- Code for an interface not an implementation
- Clear separation of concerns
There's an overhead on transforming and adapting data
However you get a more maintainable and testable application

The End

https://8thlight.com/blog/uncle-bob/2012/08/13/the-clean-architecture.html
https://www.youtube.com/watch?v=Nsjsiz2A9mg
https://martinfowler.com/bliki/InversionOfControl.html