Clean Code Cowboy by Piotr Solnica rubyconf.pt Portugal, Braga 2014 

hi I’m Piotr Solnica aka solnic github.com/solnic solnic.eu @_solnic_ 

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clean coders 

– Bob Martin from The Clean Coder book “Programmers who endure and succeed amidst swirling uncertainty and nonstop pressure share a common attribute: They care deeply about the practice of creating software. They treat it as a craft. They are professionals.” 

cowboy coders 

http://www.techrepublic.com/blog/10-things/10-types- of-programmers-youll-encounter-in-the-field/ “The Code Cowboy is a force of nature that cannot be stopped. He or she is almost always a great programmer and can do work two or three times faster than anyone else. The problem is, at least half of that speed comes by cutting corners.” 

Rules & Laws of Programming 

Single Responsibility Principle Open/closed Principle Liskov Substitution Principle Interface Segregation Principle Dependency Inversion Principle 

– DHH “I think Law of Demeter is shit” 

– 300+ angry clean coders “IT’S THE LA W!!!1111” 

who’s right? 

– nobody, ever “I always wait for the green light” 

“They’re more guidelines, than actual rules” 

code smells 

a code smell is a sign of a potential problem 

following rules rigorously is a bad practice 

the ease of refactoring is more important 

Programming with Confidence 

you know what you just wrote really works 

you know what you just changed doesn’t break anything else 

correctness verified by tests comes before concerns about implementation details 

designing interfaces is more important than implementation details 

confidence Great test coverage Continues Integration and Deployment Pair-programming Code review 

Confidence == Happiness 

Testing in Ruby == Awesome 

My testing stack rspec bogus capybara vcr 

describe Calculator do subject(:calculator) { Calculator.new } describe "#sum" do it "returns the sum of numbers" do expect(calculator.sum(2, 2)).to be(4) end end end 

feature "Home page" do scenario "as a logged-in member I can buy add-ons", js: true, vcr: true do expect(page).to have_text("5 PT classes") click_on "Add" expect(page).to have_content("1,000,00 EUR") expect(page).to have_content("Buy") click_on "Buy" expect(page).to have_text("Thanks for buying an add-on") end end Use JavaScript driver Use VCR for stubbed remote calls 

so simple! 

so awesome! 

Let’s write a failing test 

Invoices App CRUD for customers CRUD for line items CRUD for invoices 

feature "Customers" do scenario "As a user I can add a new customer and see it on the list" do visit new_customer_path find('#customer_name').set('Big Corp') find('#customer_email').set('[email protected]') find('#customer_address').set('Sunset Street 1') find('input[type=submit]').click expect(page).to have_text("Customer created") within(".customer-list") do expect(page).to have_text("Big Corp") end end end 

class CustomersController < ApplicationController def index customers = Customer.all render locals: { customers: customers } end def new customer = Customer.new render locals: { customer: customer } end def create attributes = params.require(:customer).permit(:name, :email, :address) Customer.create(attributes) redirect_to :customers, notice: "Customer created" end end 

Creating invoices 

feature "Invoices" do let!(:customer) { Customer.create(name: "Big Corp") } scenario "As a user I can create a new invoice and see it on the list" do visit new_invoice_path find("#invoice_customer_id").select("Big Corp") find("#invoice_issue_date").set("2014-10-11") find("#invoice_delivery_date").set("2014-10-11") find("#invoice_due_date").set("2014-11-11") find("input[type=submit]").click expect(page).to have_text("Invoice created") within(".invoice-list") do expect(page).to have_text("DRAFT") expect(page).to have_text("Big Corp") expect(page).to have_text("2014-10-11") expect(page).to have_text("2014-11-11") end end end 

class InvoicesController < ApplicationController def index invoices = Invoice.all render locals: { invoices: invoices } end def new invoice = Invoice.new customers = Customer.all render locals: { invoice: invoice, customers: customers } end def create attributes = params.require(:invoice).permit( :customer_id, :issue_date, :delivery_date, :due_date, :status ) Invoice.create(attributes) redirect_to :invoices, notice: "Invoice created" end end 

Turning point! 

feature "Invoices" do scenario "As a user I can create a new invoice and see it on the list", js: true do visit new_invoice_path find("#invoice_customer_id").select("Big Corp") find("#invoice_issue_date").set("2014-10-11") find("#invoice_delivery_date").set("2014-10-11") find("#invoice_due_date").set("2014-11-11") find("#line-item-id").select("Development") find("#new-item-qty").set("2") find(“#add-new-item”).click within(".item-list") do expect(page).to have_text("Development") expect(page).to have_text("200.00") end find("input[type=submit]").click expect(page).to have_text("Invoice created") within(".invoice-list") do expect(page).to have_text("DRAFT") expect(page).to have_text("Big Corp") expect(page).to have_text("2014-10-11") expect(page).to have_text("2014-11-11") expect(page).to have_text("200.00") end end end Select line item and provide quantity Make sure the total amount is present Things will happen on the client-side so we need JS Make sure the item was added to the list 

$form = $("#new_invoice") $itemSelect = $("#line-item-id") $lineItems = $("#line-items") $addButton = $("#add-new-item") $itemQty = $("#new-item-qty") $addButton.on('click', (e) -> e.preventDefault() quantity = $itemQty.val() item = $itemSelect.find(':selected').data() price = parseFloat(item.price) * parseFloat(quantity) $tr = $("").append( "#{item.name}#{item.unit}#{price}" ) $form.append( $(""). attr("type", "hidden"). attr("name", "invoice[items][][line_item_id]"). val(item.id) ) $form.append( $(""). attr("type", "hidden"). attr("name", "invoice[items][][quantity]"). val(quantity) ) $lineItems.append($tr) ) 

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BUT! 

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When it’s no longer simple to make a test pass it’s a good moment to write…more tests 

Something must create an invoice along with its line items Something must be able to calculate the total amount based on line items 

describe CreateInvoice do describe "#call" do it "creates an invoice with items" do customer = Customer.create(name: "Big Corp") magic = LineItem.create(name: 'Magic', unit: 'Hour', price: 2) healing = LineItem.create(name: 'Healing', unit: 'Hour', price: 4) today = Date.today params = { status: "DRAFT", customer_id: customer.id, issue_date: today, delivery_date: today, due_date: today + 1.month, items: [ { line_item_id: magic.id, quantity: 2 }, { line_item_id: healing.id, quantity: 3 }, ] } create_invoice = CreateInvoice.new(params) invoice = create_invoice.call expect(invoice.customer).to eql(customer) expect(invoice.line_items.to_a).to eql([magic, healing]) expect(invoice.total_amount).to eql(magic.price * 2 + healing.price * 3) end end end 

class CreateInvoice attr_reader :params def initialize(params) @params = params end def call items = params[:items] invoice = Invoice.new(params.except(:items)) items.each do |item| invoice.items.build(item) end invoice.save invoice end end 

class Invoice < ActiveRecord::Base belongs_to :customer has_many :items, class_name: "InvoiceItem" has_many :line_items, through: :items def total_amount items.map { |item| item.line_item.price * item.quantity }.sum end end BUT WAIT A MINUTE! 

LA W OF DEMETER VIOLATION! 

OK moving on… 

Let’s display an invoice 

feature "Invoices" do fixtures(:all) let(:invoice) { invoices(:first) } let(:customer) { customers(:big_corp) } scenario "as a user I can display an invoice" do visit invoices_path click_on invoice.number expect(page).to have_content(customer.name) expect(page).to have_content(invoice.number) expect(page).to have_content(invoice.issue_date) expect(page).to have_content(invoice.delivery_date) expect(page).to have_content(invoice.due_date) expect(page).to have_content(invoice.total_amount) end end missing interface! 

class Invoice < ActiveRecord::Base belongs_to :customer has_many :items, class_name: "InvoiceItem" has_many :line_items, through: :items # TODO: implement me alias_method :number, :id def total_amount items.map { |item| item.line_item.price * item.quantity }.sum end end there we go, all good 

oh noez we must display line items too! 

feature "Invoices" do fixtures(:all) let(:invoice) { invoices(:first) } let(:customer) { customers(:big_corp) } scenario "as a user I can display an invoice" do visit invoices_path click_on invoice.number expect(page).to have_content(customer.name) expect(page).to have_content(invoice.number) expect(page).to have_content(invoice.issue_date) expect(page).to have_content(invoice.delivery_date) expect(page).to have_content(invoice.due_date) expect(page).to have_content(invoice.total_amount) invoice.items.each do |item| expect(page).to have_content(item.line_item.name) expect(page).to have_content(item.line_item.price * item.quantity) end end end Demeter no likey :( 

h1 = "#{invoice.id}" table thead tr th Customer th Issue date th Delivery date th Due date th Total amount tbody tr td = invoice.customer.name td = invoice.issue_date td = invoice.delivery_date td = invoice.due_date td = number_to_currency invoice.total_amount ul - invoice.items.each do |item| li = "#{item.line_item.name} #{number_to_currency(item.line_item.price * item.quantity)}" I told you mate but you wouldn’t listen! 

OK let’s improve this 

describe InvoiceItem do fixtures(:invoice_items, :line_items) subject(:invoice_item) { invoice_items(:one) } describe "#price" do let(:line_item) { line_items(:magic) } it "returns the price based on quantity and line-item price" do expect(invoice_item.price).to eql(line_item.price * invoice_item.quantity) end end end 

class InvoiceItem < ActiveRecord::Base belongs_to :invoice belongs_to :line_item def price line_item.price * quantity end end class Invoice < ActiveRecord::Base # stuff def total_amount items.to_a.sum(&:price) end end 

the story goes on… missing Invoice#number missing validations missing print-friendly invoice page …probably more, but it’s OK 

Optimize for confidence and productiveness 

Work on your testing skills! 

Focus on correctness first 

Learn how to write tests first 

(even when writing a code spike!) 

No rules or laws, just guidelines 

Always be able to refactor with confidence 

Don’t worry be happy 

Thank you! <3<3<3 

Questions? (: 

Picture credits http://lol-rofl.com/cowboy-hat-front/ http://thankheavens.com.au/2014/01/30/quick-fresh- gluten-free-ravioli-with-vine-ripe-tomato-and-toasted- garlic-sauce/ http://www.zacksplaylist.com/bobby-mcferrin-dont- worry-be-happy-review/ http://pl.wikipedia.org/wiki/Demeter