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Building Extractable Libraries in Rails

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Hello There! I’m @patricksroberts. I work at @iorahealth. I co-organize @bostonrb.

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The Duality of a Rails Developer

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Ruby is driven by <3

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Our best practices change with our sense of beauty

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Our ecosystem is driven by the many ways to solve problems

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Rails is driven by Conventions

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Rails frees us from making many tedious decisions

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The freedom from decisions allows us unparalleled productivity

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/lib is the Battlefield

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I believe it can benefit from some conventions

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In order to ship more code I believe it can benefit from some conventions

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Namespace All The Things No Rails Application has a User class right??

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Avoid the Autoload Trap Maintain explicit entry points into your library code using initializers

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Use the Configuration Pattern Keep credentials as far away from your library code as possible

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Isolate Interaction with your Domain Use DCI at the glue points of your application code

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Namespace All The Things

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# lib/twitter_user.rb class TwitterUser def initialize(user) @user = user end end # lib/twitter_profile.rb class TwitterProfile def initialize(twitter_user, image_url) @user = twitter_user @image_url = image_url end end

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# lib/papa_smurf.rb class PapaSmurf end # lib/sleepy_smurf.rb class SleepySmurf end # lib/ninja_smurf.rb class NinjaSmurf end

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# lib/smurf.rb module Smurf class Papa end class Sleepy end class Ninja end end

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Avoiding the Autoload Trap

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Rails 3 brought a wonderful convention for removing /lib from automatically being loaded on application boot...

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... however our first instinct is to do this: # config/application.rb # Custom directories with classes and modules you want to be autoloadable. config.autoload_paths += %W(#{config.root}/lib) Let’s try something different!

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# config/initializers/twitter_wrangler.rb require_relative ‘../lib/twitter_wrangler’ # lib/twitter_wrangler.rb require ‘twitter_wrangler/authentication’ require ‘twitter_wrangler/authorization’ module TwitterWrangler end Combined with...

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We have created a namespace and setup a proper layout when we need to extract our code outside the application into a gem. ... in ten seconds or less :)

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Hide Your Credentials From Your Library

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It’s so simple to do this: # lib/twitter_wrangler.rb module TwitterWrangler OAUTH_KEY = ‘ABCDEFG1234ZXYZB2324’ end Or even this: # lib/twitter_wrangler.rb module TwitterWrangler OAUTH_KEY = ENV[‘TWITTER_KEY’] end

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But we already have an entry point for our library code. So let’s exploit the heck out of it!

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# config/initializers/twitter_wrangler.rb require_relative ‘../lib/twitter_wrangler’ TwitterWrangler.configure do |config| config.oauth_key = ENV[:twitter_oauth_key] end

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# config/initializers/twitter_wrangler.rb require_relative ‘../lib/twitter_wrangler’ TwitterWrangler.configure do |config| config.oauth_key = ENV[:twitter_oauth_key] end

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# config/initializers/twitter_wrangler.rb require_relative ‘../lib/twitter_wrangler’ TwitterWrangler.configure do |config| config.oauth_key = ENV[:twitter_oauth_key] end

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# config/initializers/twitter_wrangler.rb require_relative ‘../lib/twitter_wrangler’ TwitterWrangler.configure do |config| config.oauth_key = ENV[:twitter_oauth_key] end

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# lib/twitter_wrangler/configuration.rb module TwitterWrangler class Configuration < Struct.new(:oauth_key) end class << self attr_accessor :configuration end def self.configure self.configuration ||= Configuration.new yield(configuration) if block_given? end end

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# lib/twitter_wrangler/configuration.rb module TwitterWrangler class Configuration < Struct.new(:oauth_key) end class << self attr_accessor :configuration end def self.configure self.configuration ||= Configuration.new yield(configuration) if block_given? end end

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# lib/twitter_wrangler/configuration.rb module TwitterWrangler class Configuration < Struct.new(:oauth_key) end class << self attr_accessor :configuration end def self.configure self.configuration ||= Configuration.new yield(configuration) if block_given? end end

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# lib/twitter_wrangler/configuration.rb module TwitterWrangler class Configuration < Struct.new(:oauth_key) end class << self attr_accessor :configuration end def self.configure self.configuration ||= Configuration.new yield(configuration) if block_given? end end

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# lib/twitter_wrangler/configuration.rb module TwitterWrangler class Configuration < Struct.new(:oauth_key) end class << self attr_accessor :configuration end def self.configure self.configuration ||= Configuration.new yield(configuration) if block_given? end end

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With one additional, boilerplate class we’ve established a separation of credential concerns

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Keeping Your Domain Models Focused

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Prescriptions Queueing Authorization Authentication Timeouts Caching BMI Appointments

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Web App body mass index tweet called Library Authorization Twitter message Authentication Queueing

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ROLE

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# lib/twitter_wrangler/tweeting_patient.rb module TwitterWrangler::TweetingPatient def bmi_twitter_message “Today my BMI is #{body_mass_index} and I’m #{percent_of_body_mass_index_goal} from my goal of #{body_mass_index_goal}!” end end

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A Brief Interlude on Test Doubles

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# lib/twitter_wrangler/support/fake_patient.rb class FakePatient def body_mass_index;27;end def percent_of_body_mass_index_goal;”95%”;end def body_mass_index_goal;25;end end Option #1 - The Fake Class

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Option #2 - OpenStruct! patient = OpenStruct.new(body_mass_index: 27, percent_of_body_mass_index_goal: ’95%’, body_mass_index_goal: 25)

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Option #3 - Mock patient = mock(body_mass_index: 27, percent_of_body_mass_index_goal: ’95%’, body_mass_index_goal: 25)

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# spec/twitter_wrangler/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { FakePatient.new } before { patient.extend TweetingPatient } describe ‘#bmi_twitter_message’ do let(:tweet) { patient.bmi_twitter_message } it ‘crafts a lovely tweet’ do expect(tweet).to include ‘Today my BMI is...’ end end end

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# spec/twitter_wrangler/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { FakePatient.new } before { patient.extend TweetingPatient } describe ‘#bmi_twitter_message’ do let(:tweet) { patient.bmi_twitter_message } it ‘crafts a lovely tweet’ do expect(tweet).to include ‘Today my BMI is...’ end end end

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# spec/twitter_wrangler/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { FakePatient.new } before { patient.extend TweetingPatient } describe ‘#bmi_twitter_message’ do let(:tweet) { patient.bmi_twitter_message } it ‘crafts a lovely tweet’ do expect(tweet).to include ‘Today my BMI is...’ end end end

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# spec/twitter_wrangler/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { FakePatient.new } before { patient.extend TweetingPatient } describe ‘#bmi_twitter_message’ do let(:tweet) { patient.bmi_twitter_message } it ‘crafts a lovely tweet’ do expect(tweet).to include ‘Today my BMI is...’ end end end

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CONTEXT

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# lib/twitter_wrangler/bmi_twitter_update.rb module TwitterWrangler class BMITwitterUpdate < Struct.new(:patient) def call Queue.push tweeting_patient.bmi_twitter_message end private def tweeting_patient @tweeting_patient ||= patient.extend TweetingPatient end end end

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# lib/twitter_wrangler/bmi_twitter_update.rb module TwitterWrangler class BMITwitterUpdate < Struct.new(:patient) def call Queue.push tweeting_patient.bmi_twitter_message end private def tweeting_patient @tweeting_patient ||= patient.extend TweetingPatient end end end

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# lib/twitter_wrangler/bmi_twitter_update.rb module TwitterWrangler class BMITwitterUpdate < Struct.new(:patient) def call Queue.push tweeting_patient.bmi_twitter_message end private def tweeting_patient @tweeting_patient ||= patient.extend TweetingPatient end end end

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# lib/twitter_wrangler/bmi_twitter_update.rb module TwitterWrangler class BMITwitterUpdate < Struct.new(:patient) def call Queue.push tweeting_patient.bmi_twitter_message end private def tweeting_patient @tweeting_patient ||= patient.extend TweetingPatient end end end

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# lib/twitter_wrangler/bmi_twitter_update.rb module TwitterWrangler class BMITwitterUpdate < Struct.new(:patient) def call Queue.push tweeting_patient.bmi_twitter_message end private def tweeting_patient @tweeting_patient ||= patient.extend TweetingPatient end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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# spec/twitter_wrangler/bmi_twitter_update_spec.rb describe BMITwitterUpdate do describe ‘#call’ do let(:patient) { mock() } let(:update) { BMITwitterUpdate.new(patient) } before { Queue.stubs(:push) } it ‘extends TweetingPatient’ do update.call expect(patient).to have_received(:extend).with TweetingPatient end it ‘queues the twitter message’ do update.call expect(Queue).to have_received(:push).with patient.bmi_twitter_message end end end

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GLUE

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# app/controllers/bmi_controller.rb class BmiController < ApplicationController def create bmi = patient.bmis.create(:bmi) Resque.enqueue :bmi_twitter_update_job, patient.id respond_with bmi end private def patient @patient ||= current_user.patients.find(:patient_id) end end

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# app/jobs/bmi_twitter_update_job.rb class BmiTwitterUpdateJob @queue = :twitter def self.perform_job(patient_id) patient = Patient.find(patient_id) BMITwitterUpdate.new(patient).call end end

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RECAP

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Treat Your Lib Directory Like a Temple

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Remove Configuration Nightmares

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Protect Domain Interactions

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Thanks!