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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. I maintain @copycopter.

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I’m not so secretly using you for a sailing vacation.

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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 a Battlefield

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I think it can benefit from some conventions So we can ship some more code

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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 Models Use the DCI pattern at the glue points of your application code

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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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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 attr_accessor :oauth_key def initialize self.oauth_key = nil end 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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# lib/twitter_wrangler/roles/tweeting_patient.rb module TwitterWrangler::Roles::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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# 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 # spec/twitter_wrangler/roles/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { FakePatient.new } before { FakePatient.extend TweetingPatient } it ‘asserts some fantastic things’ do #GLORIOUS SPECS end end

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# spec/twitter_wrangler/roles/tweeting_patient_spec.rb describe TweetingPatient do let(:patient) { mock() } before do patient.stubs({body_mass_index: 27, percent_of_body_mass_index_goal: “95%” body_mass_index_goal: 25 }) patient.extend TweetingPatient end it ‘asserts some fantastic things’ do #GLORIOUS SPECS end end

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# lib/twitter_wrangler/Contexts/BMITwitterUpdate.rb module TwitterWrangler::Contexts class BMITwitterUpdate attr_reader: patient def initialize(patient) @patient = patient @patient.extend TweetingPatient end def call TwitterWranglerQueue.add @patient.bmi_twitter_message end end end

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# lib/twitter_wrangler/Contexts/BMITwitterUpdate.rb module TwitterWrangler::Contexts class BMITwitterUpdate attr_reader: patient def initialize(patient) @patient = patient @patient.extend TweetingPatient end def call TwitterWranglerQueue.add @patient.bmi_twitter_message end end end

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# lib/twitter_wrangler/Contexts/BMITwitterUpdate.rb module TwitterWrangler::Contexts class BMITwitterUpdate attr_reader: patient def initialize(patient) @patient = patient @patient.extend TweetingPatient end def call TwitterWranglerQueue.add @patient.bmi_twitter_message end end end

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# lib/twitter_wrangler/Contexts/BMITwitterUpdate.rb module TwitterWrangler::Contexts class BMITwitterUpdate attr_reader: patient def initialize(patient) @patient = patient @patient.extend TweetingPatient end def call TwitterWranglerQueue.add @patient.bmi_twitter_message end end end

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# spec/models/patient_bmi_observer_spec.rb describe PatientBMIObserver do let(:bmi_update) { mock() } before do BMITwitterUpdate.stubs(:new).returns bmi_update bmi_update.stubs :call end it ‘sends a twitter update on mah BMI’ do # expect #call to have been called once end end

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# spec/models/patient_bmi_observer_spec.rb describe PatientBMIObserver do let(:bmi_update) { mock() } before do BMITwitterUpdate.stubs(:new).returns bmi_update bmi_update.stubs :call end it ‘sends a twitter update on mah BMI’ do # expect #call to have been called once end end

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Provides clear separation of Domain Model and outside code Creates isolatable tests Easy path forward for gem extraction Boilerplate :( YAGNI :(

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Thanks!

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Questions? I only take questions in the form of answers OR in haiku