Service Objects

Version #1

http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/

class UserAuthenticator
  def initialize(user)
    @user = user
  end

  def authenticate(unencrypted_password)
    return false unless @user

    if BCrypt::Password.new(@user.password_digest) == unencrypted_password
      @user
    else
      false
    end
  end
end

class SessionsController < ApplicationController
  def create
    user = User.where(email: params[:email]).first

    if UserAuthenticator.new(user).authenticate(params[:password])
      self.current_user = user
      redirect_to dashboard_path
    else
      flash[:alert] = "Login failed."
      render "new"
    end
  end
end

Version #2

http://jamesgolick.com/2010/3/14/crazy-heretical-and-awesome-the-way-i-write-rails-apps.html

class UserCreationService
  def initialize(user_klass = User, log_klass = Log)
    @user_klass = user_klass
    @log_klass  = log_klass
  end

  def create(params)
    @user_klass.create(params).tap do |u|
      @log_klass.new_user(u)
    end
  end
end

describe UserCreationService do
  before do
    @user       = stub("User")
    @user_klass = stub("Class:User", :create   => @user)
    @log_klass  = stub("Class:Log",  :new_user => nil)
    @service    = UserCreationService.new(@user_klass, @log_klass)
    @params     = {:name => "Matz", :hobby => "Being Nice"}
    @service.create(@params)
  end

  it "creates the user with the supplied parameters" do
    @user_klass.should have_received(:create).with(@params)
  end

  it "logs the creation of the user" do
    @log_klass.should have_received(:new_user).with(@user)
  end
end

Before

class User < ActiveRecord::Base
  after_create :log_creation

  protected
    def log_creation
      Log.new_user(self)
    end
end

Version #3

http://www.naildrivin5.com/blog/2012/06/10/single-responsibility-principle-and-rails.html

class ApplicationUserCreator
  def initialize(welcome_mailer=nil)
    @welcome_mailer = welcome_mailer
  end

  def create_new_user(params)
    User.create(params).tap { |new_user|
      if new_user.valid?
        self.welcome_mailer.deliver_welcome_email(new_user)
      end
    }
  end

private

  def welcome_mailer
    @welcome_mailer ||= UserMailer
  end
end

class AdminUsersController < ApplicationController
  def create
    @user = ApplicationUserCreator.new(AdminUserMailer).create_new_user(params[:user])
  end
end

Before

class UsersController < ApplicationController
  def create
    @user = User.new(params[:user])
    respond_to do |format|
      if @user.save
        UserMailer.deliver_welcome_email(@user)
      end
    end
  end
end

Version #4

http://slides.jcoglan.com/di-eurucamp

class Github::Client
  def initialize(http_client)
    @http = http_client
  end

  def get_user(name)
    data = @http.get("/users/#{name}").json_data
    Github::User.new(data)
  end
end

Version #5

(Service layer)

http://slides.jcoglan.com/di-eurucamp

class Services::ConcertsClient
  def initialize(http_client)
    @http = http_client
  end

  def find(id)
    data = @http.get("/concerts/#{id}").json_data
    Models::Concert.new(data)
  end
end

class Models::Concert
  def initialize(data)
    @json_data = data
  end

  def name
    @json_data['name']
  end

  def headliners
    @json_data['performances'].
        select { |p| p['billing'] == 'headline' }.
        map { |p| Models::Artist.new(p['artist']) }
  end
end

module Services
  def self.concerts
    @concerts ||= begin
                    uri  = 'http://concerts-service'
                    http = HTTPClient.new(uri)
                    ConcertsClient.new(http)
                  end
  end
end

concert = Services.concerts.find(params[:id])

Version #6

• https://speakerdeck.com/seenmyfate/4-steps-to-faster-rails-tests
• http://confreaks.com/videos/641-gogaruco2011-fast-rails-tests

class DiscountCalculator
  def total_discount(items)
    items.collect(&:discount).inject(:+)
  end
end

class Basket < ActiveRecord::Base
  has_many :basket_items

  def total_discount
    DiscountCalculator.new.total_discount(basket_items)
  end
end

Version #7

(Use case objects)

https://gist.github.com/2838490

class PostComment
  def initialize(user, entry, attributes)
    @user = user
    @entry = entry
    @attributes = attributes
  end
 
  def post
    @comment = @user.comments.new
    @comment.assign_attributes(@attributes)
    @comment.entry = @entry
    @comment.save!
 
    LanguageDetector.new(@comment).set_language
    SpamChecker.new(@comment).check_spam
    CommentMailer.new(@comment).send_mail
 
    post_to_twitter  if @comment.share_on_twitter?
    post_to_facebook if @comment.share_on_facebook?
 
    @comment
  end
 
  private
 
  def post_to_twitter
    PostToTwitter.new(@user, @comment).post
  end
 
  def post_to_facebook
    PostToFacebook.new(@user, @comment).action(:comment)
  end
end