Clean Architecture - Arena TOTVS 2015

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CLEAN ARCHITECTURE ON RAILS

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CHAPTER I What is Clean Architecture?

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the PROBLEM

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your top level structure is screaming the web FRAMEWORK

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The web is a delivery mechanism

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the web is a COMMODITY

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yet it DOMINATES your code

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image you’ve just joined a PROJECT

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what makes a GOOD architecture?

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it is not about frameworks and tools

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Fabiano Beselga CTO magnetis.com.br WRITER medium.com/@fbzga TWITTER @fbzga

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bit.ly/clean-rails

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IVAR JACOBSON

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business rules INTERACTORS (aka use cases)

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domain model ENTITIES

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communication interfaces BOUNDARIES

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diagrams: Robert C Martin

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What about MVC?

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MVC as a Web architecture

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this is NOT WHAT I MEANT

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WEB FRAMEWORK APP

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CHAPTER II HOW to use it with Rails?

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BRAAVOS

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WE ARE OPENING A BANK! WE NEED TO HIRE A GREAT DEVELOPER!

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WHAT ABOUT THIS ONE?

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HIRED!

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ﬁrst day at WORK

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THE SYSTEM MUST TRANSFER MONEY BETWEEN THE FAMILIES ACCOUNTS

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OK! ANY EXCEPTION COURSES?

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WHEN THERE ISN’T ENOUGH MONEY TO TRANSFER.

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that’s easy, I can do it in 7 STEPS!

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GREAT! YOU HAVE 10 MINUTES!

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challenge accepted!

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1 create the PROJECT

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rails new braavos

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mkdir core

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module Core end core.rb

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2 deﬁne BOUNDARIES

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README Driven Development

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Usage Transfer money Core.transfer_money(amount: 10_000, source_account_id: 1, destination_account_id: 2) README => true # when transfer successful => false # when not enough balance

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3 deﬁne behaviour Driven Development

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context 'enough money to transfer' do it 'responds true' do expect(transfer).to be true end it 'debits the source account' do expect{ transfer }.to change{ source_account_balance }.by(- amount) end it 'credits the destination account' do expect{ transfer }.to change{ destination_account_balance }.by(amount) end end PRIMARY course

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context 'not enough money to transfer' do it 'cancels the transfer and responds false' do expect(transfer).to be false end it 'does not change the accounts balance' do expect{ transfer }.to_not change{ source_account_balance } expect{ transfer }.to_not change{ destination_account_balance } end end EXCEPTION COURSE

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FFF

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deﬁne DATA MODEL 4

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CAN YOU TELL ME A LITTLE MORE ABOUT THE DOMAIN?

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EACH FAMILY HAS AN ACCOUNT. EACH ACCOUNT HAS A HISTORY OF TRADES MADE.

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rails g model account name rails g model trade account:references amount:decimal date:date

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trades debit: -1000 credit: +1000

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the ENTRY POINT 5

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module Core class << self delegate :transfer_money, to: TransferMoney end end core.rb

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the USE CASE 6

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module Core class TransferMoney def self.transfer_money(source_account_id:, destination_account_id:, amount:) balance = Core.get_balance(account_id: source_account_id) return false if balance < amount ActiveRecord::Base.transaction do Trade.create!(account_id: source_account_id, amount: -amount) Trade.create!(account_id: destination_account_id, amount: amount) end end end end core/transfer_money.rb

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…

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REFACTOR!

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module Core class << self delegate :transfer_money, to: TransferMoney end end core.rb before

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CAZE DSL to elegantly declare use cases

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Gemfile gem 'caze'

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module Core include Caze has_use_case :transfer_money, TransferMoney end core.rb AFTER

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module Core include Caze has_use_case :transfer_money, TransferMoney, transactional: true end core.rb AFTER

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g github.com/magne/s/caze

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BREAKING NEWS!   WE HAVE MONEY TO HIRE AGAIN!

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WHAT ABOUT THIS SNOW?

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WHAT?

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Usage Transfer money Core.transfer_money(amount: 10_000, source_account_id: 1, destination_account_id: 2) README => true # when transfer successful => false # when not enough balance

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expose it to the web 7

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let’s call it on a CONTROLLER

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class TransferMoneyController < ApplicationController before_action :load_balance def create if Core.transfer_money(source_account_id: source_account_id, destination_account_id: destination_account_id, amount: amount) redirect_to new_transfer_money_path else flash[:error] = 'Not enough money on the source account' render :new end end private def load_balance @balance = Core.get_balance(account_id: current_account_id) end end

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bit.ly/braavos

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what just happened?

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Core represents WHAT THE SYSTEM Does CHANGES

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core/ get_balance.rb transfer_money.rb BEHAVIOUR CHANGES

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the models represent WHAT THE SYSTEM IS STABLE

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app/ models/ account.rb trade.rb DATA STABLE

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a key, longstanding hallmark of a good program is that it separates what is stable from what changes in the interest of good maintenance. - Trygve Reenskaug

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Models Core Rails delivery mechanism behaviour MODULE data #1

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the ALTERNATIVES

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Models Core Rails delivery mechanism behaviour RAILS ENGINE #2

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The database is a detail

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Isolate it!

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Models Core Rails delivery mechanism behaviour gem rails engine data API #3

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what about real life?

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magnetis.com.br

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~ 4 years old codebase

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experimenting with clean architecture ~ 2 years

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the ﬁrst seeds magnetis core

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a module for each DOMAIN CONCEPT

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we have a module for investments recommendation Advisor

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Advisor.recommend_investments(params)

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we have a module for accounting Accountant

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magnetis/ domain/ accountant/ advisor/

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BOUNDED CONTEXTs Advisor Accountant Order Manager Account Manager Trader Pricing Backtesting

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why not MICROSERVICES?

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we also use the Rails WAY

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FINAL CHAPTER when to use it?

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YOUR PRODUCT

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core business your product rails way clean architecture

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Eric Evans Don’t try yo apply DDD to everything. Draw a context map and decide on where you will make a push for DDD and where you will not .

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THE distance from the view

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the domain logic is close to the view Rails way

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the domain logic is far from the view Clean architecture

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TIMING

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image: Kent Beck

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Lessons learned

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no good

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Over-engineering when the domain logic is close to the view

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getting out of the rails conventions may be hard

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the cool STUFF

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defer decisions until the last responsible moment

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it SCREAMS BEHAVIOR

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decoupled business rules

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tests RUNNING FASTER!

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what makes a GOOD architecture?

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CLEAN ARCHITECTURE HEXAGONAL ARCHITECTURE DOMAIN DRIVEN DESIGN DATA CONTEXT INTERACTION TRAILBLAZER

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all these architectures have SIMILAR OBJECTIVES

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Architecture is about Intent

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Intent = what the SYSTEM DOES

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reflect THE USER’S MENTAL MODEL in your architecture

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domain as a 1st class citizen

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ONE MORE THING…

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we are hiring fabiano@magne/s.com.br magne/s.com.br/dev

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Developer #1 Developer #2 The Boss The Mastermind Tio Roberto Domain Father Advisor Presenter CAST TYRION LANNISTER Jon SNOW SHERKLOCKS’ BROTHER IVAR JACOBSON UNCLE BOB ERIC EVANS ROBERT DUVAL FABIANO BESELGA by @fbzga