Maintainable Templates

<h3>Your Saved Credit Card</h3>

<dl>
  <dt>Number</dt>
  <dd>XXXX-XXXX-XXXX-<%= @credit_card.number[-4..-1] %></dd>
  <dt>Exp. Date</dt>
  <dd>
    <%= @credit_card.expiration_month %> / <%= @credit_card.expiration_year %>
  </dd>
</dl>

Repeated logic in another template

<p>
  Thanks for ordering! Your purchase has been billed to your credit card:
  <strong>XXXX-XXXX-XXXX-<%= @order.credit_card.number[-4..-1] %></strong>
</p>

Other views with the same logic

...are inevitable.

Helpers

View Helpers live in app/helpers and provide small snippets of reusable code for views.

Rails Guides

Defining helpers

module CreditCardHelper
  def masked_credit_card_number(number)
    "XXXX-XXXX-XXXX-" + number[-4..-1]
  end
end

Using helpers

<p>
  Thanks for ordering! Your purchase has been billed to your credit card:
  <strong><%= masked_credit_card_number(@credit_card.number) %></strong>
</p>

Problems with helpers

Big projects end up with tons
Difficult to organize
Complex logic isn't well suited for them
Don't feel right

Decorator Pattern

[Decorators] attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Design Patterns: Elements of Reusable Object-Oriented Software

Traits of a Decorator

Wraps a single object
Transparent interface
Forwards methods to original object

In our case:

Adds presentational logic to models without affecting the model itself

Implementing a Decorator in Ruby

class Decorator
  def initialize(component)
    @component = component
  end

  def method_missing(method, *arguments, &block)
    if @component.respond_to?(method)
      @component.send(method, *arguments, &block)
    else
      super
    end
  end

  def respond_to_missing?(method, *)
    @component.respond_to?(method) || super
  end
end

Credit Card Decorator

class CreditCardDecorator < Decorator
  def masked_number
    "XXXX-XXXX-XXXX-" + number[-4..-1]
  end

  # ... other presentational methods
end

Instantiating the decorator

class CreditCardsController < ApplicationController
  def show
    @credit_card = CreditCardDecorator.new(
      current_user.credit_cards.find(params[:id])
    )
  end
end

Using the decorator

<p>
  Thanks for ordering! Your purchase has been billed to your credit card:
  <strong><%= @credit_card.masked_number %></strong>
</p>

Mmmm, that's nice.

When to decorate

Presentation logic that relates directly to a single instance of a model.

Draper

Implementing basic decorators is easy, but Draper adds a few helpful features:

Access to the view context
Easily decorate collections
Pretends to be decorated object (helpful for form_for and such)
Easily decorate associations

Complex views

Unique and/or complex UI behavior will quickly outgrow helpers.

Complex view example

<dl class="story-summary">
  <dt>Assigned to</dt>
  <dd>
    <% if @story.assigned_user == current_user %>
      You
    <% else %>
      <%= @story.assigned_user.name %>
    <% end %>
  </dd>
  <dt>Participants</dt>
  <dd><%= @story.participants.reject { |p| p == current_user }.map(&:name).join(", ") %></dd>
</dl>

Presentation Model

The essence of a Presentation Model is of a fully self-contained class that represents all the data and behavior of the UI window, but without any of the controls used to render that UI on the screen. A view then simply projects the state of the presentation model onto the glass.

Martin Fowler

Learning from JavaScript libraries

Thanks, Backbone.

Designing a view object

class StorySummaryView
  def initialize(template, story, current_user)
    @template = template
    @story = story
    @current_user = current_user
  end

  def assigned_user
    if @story.assigned_user == @current_user
      "You"
    else
      @story.assigned_user.name
    end
  end

  def participant_names
    participants.map(&:name).join(", ")
  end

  def to_s
    @template.render(partial: "story_summary", object: self)
  end

  private

  def participants
    @story.participants.reject { |p| p == @current_user }
  end
end

Story summary template

<dl class="story-summary">
  <dt>Assigned to</dt>
  <dd><%= story_summary.assigned_user %></dd>
  <dt>Participants</dt>
  <dd><%= story_summary.participant_names %></dd>
</dl>

Helpers to set up view objects

module StoriesHelper
  def story_summary(story)
    StorySummaryView.new(self, story, current_user)
  end
end

In our calling view:

<%= story_summary(@story) %>

Form Builders

Rails comes with View Objects.

`form_for`

<%= form_for @user do |form| %>
  <div class="form-field">
    <%= form.label :name %>
    <%= form.text_field :name %>
  </div>

  <div class="form-field">
    <%= form.label :email %>
    <%= form.text_field :email %>
  </div>
<% end %>

Defining a custom FormBuilder

class FancyFormBuilder < ActionView::Helpers::FormBuilder
  def fancy_text_field(attribute, options = {})
    @template.content_tag(:div, class: "form-field") do
      label(attribute) + text_field(attribute, options)
    end
  end
end

Rendering the custom builder

<%= form_for @user, builder: FancyFormBuilder do |form| %>
  <%= form.fancy_text_field :name %>
  <%= form.fancy_text_field :email %>
<% end %>

Other tips

Use i18n
Find gems to do this work for you (eg. simple_form, table_cloth)

Thanks!

Questions or Comments?