#287 Presenters from Scratch pro

Oct 03, 2011 | 14 minutes | Views, Refactoring

Clean up complex view logic with the help of presenters, and doing this from scratch gives you a lot of flexibility. Here I show not only how to create presenters, but how to test them using Test Unit and RSpec.

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Note: In the episode I reversed the parameters in the ApplicationController#present method. See below for the fixed code.

          app/presenters/user_presenter.rb
        
class UserPresenter < BasePresenter
  presents :user
  delegate :username, to: :user

  def avatar
    site_link image_tag("avatars/#{avatar_name}", class: "avatar")
  end

  def linked_name
    site_link(user.full_name.present? ? user.full_name : user.username)
  end

  def member_since
    user.created_at.strftime("%B %e, %Y")
  end

  def website
    handle_none user.url do
      h.link_to(user.url, user.url)
    end
  end

  def twitter
    handle_none user.twitter_name do
      h.link_to user.twitter_name, "http://twitter.com/#{user.twitter_name}"
    end
  end

  def bio
    handle_none user.bio do
      markdown(user.bio)
    end
  end

private

  def handle_none(value)
    if value.present?
      yield
    else
      h.content_tag :span, "None given", class: "none"
    end
  end

  def site_link(content)
    h.link_to_if(user.url.present?, content, user.url)
  end

  def avatar_name
    if user.avatar_image_name.present?
      user.avatar_image_name
    else
      "default.png"
    end
  end
end

          app/presenters/base_presenter.rb
        
class BasePresenter
  def initialize(object, template)
    @object = object
    @template = template
  end

private

  def self.presents(name)
    define_method(name) do
      @object
    end
  end

  def h
    @template
  end

  def markdown(text)
    Redcarpet.new(text, :hard_wrap, :filter_html, :autolink).to_html.html_safe
  end
  
  def method_missing(*args, &block)
    @template.send(*args, &block)
  end
end

          application_helper.rb
        
module ApplicationHelper
  def present(object, klass = nil)
    klass ||= "#{object.class}Presenter".constantize
    presenter = klass.new(object, self)
    yield presenter if block_given?
    presenter
  end
end

          application_controller.rb
        
def present(object, klass = nil)
  klass ||= "#{object.class}Presenter".constantize
  klass.new(object, view_context)
end

          app/views/users/show.html.erb
        
<% present @user do |user_presenter| %>
  <div id="profile">
    <%= user_presenter.avatar %>
    <h1><%= user_presenter.linked_name %></h1>
    <dl>
      <dt>Username:</dt>
      <dd><%= user_presenter.username %></dd>
      <dt>Member Since:</dt>
      <dd><%= user_presenter.member_since %></dd>
      <dt>Website URL:</dt>
      <dd><%= user_presenter.website %></dd>
      <dt>Twitter Name:</dt>
      <dd><%= user_presenter.twitter %></dd>
      <dt>Bio:</dt>
      <dd><%= user_presenter.bio %></dd>
    </dl>
  </div>
<% end %>

          test/unit/presenters/user_presenter_test.rb
        
class UserPresenterTest < ActionView::TestCase
  test "says when none given" do
    presenter = UserPresenter.new(User.new, view)
    assert_match "None given", presenter.website
  end
end

          spec/presenters/user_presenter_spec.rb
        
describe UserPresenter do
  it "says when none given" do
    presenter = UserPresenter.new(User.new, view)
    presenter.website.should include("None given")
  end
end

          spec/spec_helper.rb
        
RSpec.configure do |config|
  config.include ActionView::TestCase::Behavior, example_group: {file_path: %r{spec/presenters}}
end