Objects on Rails - Speaker Deck

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OBJECTS ON RAILS Lailson Bandeira

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Conteúdo avançado

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WHOAMI Lailson Bandeira Co-founder of Guava Software Co-founder Frevo on Rails MS.c. in Machine Learning at CIn/UFPE Member of the VIISAR Research Group Sun Certified Java Programmer (SCJP)

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M V C

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M C V

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Fat controllers

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Skinny controllers, fat models

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Bullshit!

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You’ll talk about concerns, right?

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Noooooo!

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PRESENTER aka Exhibit aka View Model

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PRESENTER DEFINITION Presenters objects are a type of decorator specialized for presenting models to an end user. — Avdi Grimm M C V

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PRESENTER LONG DEFINITION If the Model is concerned with storing and manipulating business data, and the View is concerned with displaying it, you can think of the Exhibit as standing between them deciding which data to show, and in what order. It may also provide some extra presentation-specific information (such as the specific URLs for related re- sources) which the business model has no knowledge of by itself. — Avdi Grimm

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PRESENTER WHEN TO USE IT Use it when you have complex presentation rules.

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PRESENTER WHEN TO USE IT Presenters are the ideal place to: • format complex data for user display • define commonly-used representations of an object • mark up attributes with a little semantic HTML — Draper

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PRESENTER EXAMPLE # app/helpers/articles_helper.rb def publication_status(article) if article.published? "Published at #{article.published_at.strftime('%A, %B %e')}" else "Unpublished" end end

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PRESENTER # app/decorators/article_decorator.rb class ArticleDecorator < Draper::Decorator delegate_all ! def publication_status if published? "Published at #{published_at}" else "Unpublished" end end ! def published_at object.published_at.strftime("%A, %B %e") end end EXAMPLE

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PRESENTER # app/controllers/articles_controller.rb def show @article = Article.find(params[:id]).decorate end ! # view <%= @article.publication_status %> EXAMPLE

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PRESENTER LIBRARIES • draper https://github.com/drapergem/draper ! • cells https://github.com/apotonick/cells • DIY with Forwardables

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FORM OBJECT

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FORM OBJECT DEFINITION Form objects decouple your models from forms. They usually perform validations, setup of nested models, rendering of form helpers and coordination of object relations. — Nick Sutterer M C V

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FORM OBJECT WHEN TO USE IT Use it when when you have a form which doesn’t match your models.

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FORM OBJECT EXAMPLE # models ! class User < ActiveRecord::Base has_one :profile end ! class Profile < ActiveRecord::Base belongs_to :user end

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FORM OBJECT EXAMPLE # form class UserForm < Reform::Form include DSL include Reform::Form::ActiveModel ! properties [:first_name, :last_name], on: :user properties [:email, :locale, :age], on: :profile ! model :user, on: :user ! validates :first_name, :last_name, :email, presence: true end

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FORM OBJECT EXAMPLE class UsersController < ApplicationController def new @form = Forms::UserForm.new(user: User.new, profile: Profile.new) end ! def create if form.validate(params) form.save do |data, map| user = User.create(map[:user]) map[:user_id] = user.id Profile.create(map[:profile]) end else render action: :new end end end

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FORM OBJECT • reform https://github.com/apotonick/reform ! • bureaucrat https://github.com/tizoc/bureaucrat • DIY with virtus  https://github.com/solnic/virtus LIBRARIES

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VALIDATOR

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VALIDATOR DEFINITION Validator is an object that validates one or more objects. — Unknown author M C V

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WHEN TO USE IT Use it when you have complex validation rules, possible spanning multiple objects or when you have contextual validation. VALIDATOR

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EXAMPLE # models ! class Article < ActiveRecord::Base # attrs title, body, status end VALIDATOR

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EXAMPLE class Edit < Scrivener attr_accessor :title attr_accessor :body ! def validate assert_present :title assert_present :body end end ! edit = Edit.new(title: title, body: body) edit.valid? #=> true ! article = Article.new(edit.attributes) article.save VALIDATOR

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EXAMPLE class Publish < Scrivener attr_accessor :status ! def validate assert_format :status, /^(published|draft)$/ end end ! publish = Publish.new(status: "published") publish.valid? #=> true ! article.update_attributes(publish.attributes) VALIDATOR

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• scrivener https://github.com/soveran/scrivener ! • vanguard https://github.com/mbj/vanguard • DIY with active_model LIBRARIES VALIDATOR

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POLICY

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POLICY DEFINITION Policy is an object that encapsulates permission business rules. — Me M C V

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POLICY WHEN TO USE IT Use it when your application has complex domain/business rules.

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POLICY EXAMPLE class InvestmentPromotionPolicy attr_reader :investment ! def initialize(investment) @investment = investment end ! def promoted? valid_promotion_date? and owner_promotable? end ! def owner_promotable? investment.owner.active_for_promotion? end ! def promotion_status case when promoted? :promoted when valid_promotion_date? and !owner_promotable? :pending_for_promotion else :not_promoted end end ! def valid_promotion_date? (investment.promotion_starts_at..investment.promotion_ends_at).cover? Time.now end end

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POLICY EXAMPLE class Investment < ActiveRecord::Base delegate :promoted?, :owner_promotable?, :promotion_status to: :promotion_policy ! # some methods ! private ! def promotion_policy @promotion_policy ||= InvestmentPromotionPolicy.new(self) end end

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POLICY EXAMPLE 2 class PostPolicy attr_reader :user, :post ! def initialize(user, post) @user = user @post = post end ! def update? user.admin? or not post.published? end end

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POLICY EXAMPLE 2 # controller def update @post = Post.find(params[:id]) authorize @post if @post.update(post_params) redirect_to @post else render :edit end end

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POLICY • pundit https://github.com/elabs/pundit ! • DIY with POROs LIBRARIES

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INTERACTOR aka Service aka Workflow aka Use Case

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INTERACTOR DEFINITION An interactor is an object with a simple interface and a singular purpose. It provides a common interface for performing complex interactions in a single request and usually represents a business process. — Collective Idea M C V

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INTERACTOR WHEN TO USE IT Use it when your application complex domain/business process.

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INTERACTOR EXAMPLE class AuthenticateUser include Interactor ! def perform if user = User.authenticate(context[:email], context[:password]) context[:user] = user else context.fail! end end end

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INTERACTOR EXAMPLE class SessionsController < ApplicationController def create result = AuthenticateUser.perform(session_params) ! if result.success? redirect_to result.user else render :new end end ! private def session_params params.require(:session).permit(:email, :password) end end

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INTERACTOR EXAMPLE class PlaceOrder include Interactor::Organizer ! organize [ CheckInventory, CalculateTax, ChargeCard, CreateOrder, DeliverThankYou, DeliverOrderNotification, ScheduleFollowUp ] end

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INTERACTOR • interactor https://github.com/collectiveidea/interactor ! • mutations https://github.com/cypriss/mutations ! • DIY with POROs LIBRARIES

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QUERY

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QUERY DEFINITION Query is an object that implements an interface for querying the database. — Luca Guidi M C V

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QUERY WHEN TO USE IT Use it when your application business rules requires complex queries.

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QUERY class MediaQuery attr_reader :start_date, :end_date, :term, :location_name ! def initialize(params={}) @start_date = params[:start_date] @end_date = params[:end_date] @term = params[:term] @location_name = params[:location_name] end ! def generate query = Medium.scoped query = query.gte(created_at: start_date) if start_date query = query.lte(created_at: end_date) if end_date query = query.where(location: location_name) if location_name.present? query = query.text(term) if term.present? query end ! end EXAMPLE

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QUERY EXAMPLE • arel https://github.com/rails/arel ! • origin https://github.com/mongoid/origin ! • DIY with POROs

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REFERENCES • 7 Ways to Decompose Fat ActiveRecord Models http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/ ! • Structuring Rails Applications http://karolgalanciak.com/blog/2013/10/06/structuring-rails-applications/ ! • Concerns, Decorators, Presenters, Service Objects, Helpers, Help Me Decide! http://confreaks.com/videos/3329-railsconf-concerns-decorators-presenters-service-objects-helpers-help-me-decide ! • Catalog of Patterns of Enterprise Application Architecture http://martinfowler.com/eaaCatalog/

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That’s all, folks! XXI FREVO ON RAILS MEETUP Slides presented by Lailson Bandeira on July 26, 2014 as part of the 21st Frevo on Rails Meetup, available at https://speakerdeck.com/lailsonbm. Slides created with Keynote with the fonts Monserrat, Source Sans Pro and Inconsolata. LAILSON BANDEIRA http://lailson.me/ http://github.com/lailsonbm http://facebook.com/guavasoftware