Hexagonal Rails Part 1

Or, 7 Patterns to Refactor Fat ActiveRecord Models

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

Value Objects

Objects whose equality is dependent on their value rather than an identity

class Rating
  include Comparable

  def self.from_cost(cost)
    if cost <= 2
      new("A")
    elsif cost <= 4
      new("B")
    elsif cost <= 8
      new("C")
    elsif cost <= 16
      new("D")
    else
      new("F")
    end
  end

  def initialize(letter)
    @letter = letter
  end

  def better_than?(other)
    self > other
  end

  def <=>(other)
    other.to_s <=> to_s
  end

  def hash
    @letter.hash
  end

  def eql?(other)
    to_s == other.to_s
  end

  def to_s
    @letter.to_s
  end
end

Form Objects

Translation layer between forms and the models that are accessed.

class Signup
  include Virtus

  extend ActiveModel::Naming
  include ActiveModel::Conversion
  include ActiveModel::Validations

  attr_reader :user
  attr_reader :company

https://github.com/apotonick/reform

https://github.com/solnic/virtus

Service Objects

An object that encapsulates one or more discrete business level operations.

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

View Objects

If logic is needed purely for display purposes, it does not belong in the model.

class DonutChart
  def initialize(snapshot)
    @snapshot = snapshot
  end

  def cache_key
    @snapshot.id.to_s
  end

  def data
    # pull data from @snapshot and turn it into a JSON structure
  end
end

Query Objects

Each query object is responsible for returning a result set based on business rules.

class AbandonedTrialQuery
  def initialize(relation = Account.scoped)
    @relation = relation
  end

  def find_each(&block)
    @relation.
      where(plan: nil, invites_count: 0).
      find_each(&block)
  end
end

AbandonedTrialQuery.new.find_each do |account|
  account.send_offer_for_support
end

Decorators

Let you layer on functionality to existing operations.

class FacebookCommentNotifier
  def initialize(comment)
    @comment = comment
  end

  def save
    @comment.save && post_to_wall
  end

  def post_to_wall
    Facebook.post(title: @comment.title, user: @comment.author)
  end
end

class CommentsController < ApplicationController
  def create
    @comment = FacebookCommentNotifier.new(Comment.new(params[:comment]))

    if @comment.save
      redirect_to blog_path, notice: "Your comment was posted."
    else
      render "new"
    end
  end
end

Policy Objects

Policy Objects encapsulate one business rule

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

  def active?
    @user.email_confirmed? &&
    @user.last_login_at > 14.days.ago
  end
end