Definitions

Decorator

In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.

src: Wikipedia

class UserDecorator
  def full_name
    [object.first_name, object.last_name].join(' ')
  end
end

Presenter

The Presenter pattern addresses bloated controllers and views containing logic in concert by creating a class representation of the state of the view.

src: Jay Fields' Thoughts

Exhibit

The primary goal of exhibits is to connect a model object with a context for which it's rendered.

src: Wikipedia

Presentation Model

In this pattern there is no Presenter. Instead the View binds directly to a Presentation Model. The Presentation Model is a Model crafted specifically for the View. 

This means this Model can expose properties that one would never put on a domain model as it would be a violation of separation-of-concerns.

src: Stack Overflow

CQ Manager

(examples)

class DishDecorator < Draper::Decorator
  include Draper::LazyHelpers
  
  delegate_all

  def belongs_to_current_user?
    object.user == current_user
  end

  def order_by_current_user?
    object.order.user == current_user
  end

  def table_buttons
    (edit_button.to_s + delete_button.to_s + copy_button.to_s).html_safe
  end

  def edit_button
    if (belongs_to_current_user? && !order.delivered?) ||
        (order_by_current_user? && order.ordered?)
      link_to 'Edit', edit_order_dish_path(order, object), class: 'margin-right-small'
    end
  end

  def delete_button
    if belongs_to_current_user? && order.in_progress?
      link_to 'Delete', order_dish_path(order, object), method: :delete
    end
  end
  
  ...
end

tr
  th= dish.user.name
  th= dish.name
  th= dish.price
  th= dish.table_buttons

Result

class DishDecorator < Draper::Decorator
  include Draper::LazyHelpers

  delegate_all

  def belongs_to_current_user?
    object.user == current_user
  end

  def order_by_current_user?
    object.order.user == current_user
  end
end

class DishPresenter
  include Rails.application.routes.url_helpers
  include ActionView::Helpers

  attr_reader :dish, :current_user

  def initialize(dish, current_user)
    @dish = dish
    @current_user = current_user
  end

  def table_buttons
    (edit_button.to_s + delete_button.to_s + copy_button.to_s).html_safe
  end

  def edit_button
    if (dish.belongs_to_current_user? && !dish.order.delivered?) ||
        (dish.order_by_current_user? && dish.order.ordered?)
      link_to 'Edit', edit_order_dish_path(dish.order, dish), class: 'margin-right-small'
    end
  end

  def delete_button
    if dish.belongs_to_current_user? && dish.order.in_progress?
      link_to 'Delete', order_dish_path(dish.order, dish), data: {confirm: 'Are you sure?'}, method: :delete
    end
  end

  def copy_button
    if (!dish.belongs_to_current_user? && dish.order.in_progress?)
      link_to 'Copy', copy_order_dish_path(dish.order, dish), data: {confirm: 'This will overwrite your current dish! Are you sure?'}
    end
  end
end

- presenter = DishPresenter.new dish, current_user
tr
  th= dish.user.name
  th= dish.name
  th= dish.price
  th= presenter.table_buttons

or

class DishDecorator < Draper::Decorator
  include Draper::LazyHelpers

  delegate_all

  ...

  def presenter
    @presenter ||= DishPresenter.new self, current_user
  end
end

Gains

• Easier testing
• Smaller classes
• Better decorator reusability
• Less bloated decorator

src: Wikipedia

Changes

Github commit