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Presenters and Decorators A Code Tour

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No content

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Mike Moore

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@blowmage

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Disclaimer

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Presenters should ease PAIN

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Components...

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<%= render_component(@component) %> app/views/dashboard/index.html.erb

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def render_component(component) render :partial => "shared/component", :locals => {:component => component} end app/controllers/application_controller.rb

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<%= render_component(component) %> app/views/shared/_component.html.erb

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module ComponentHelper def render_component(component) return "" if component.nil? if component.respond_to?(:render) raw component.render(self) else raw component.to_s end end end app/helpers/component_helper.rb

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class DashboardController < ApplicationController before_filter :require_user def index @component = DashboardComponentBuilder.build(current_user) end end app/controller/dashboard_controller.rb

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class DashboardComponentBuilder def self.build(user) my_posts = user.posts.recent DashboardComponent.new( :post_items => PostItemComponentBuilder.build_list(my_posts), :author_stats_component => AuthorAnalyticsComponentBuilder.build(user) ) end end lib/dashboard_component_builder.rb

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class PostItemComponentBuilder < ComponentBuilder def self.build(post) post_path = UrlGenerator.post_path(post) PostItemComponent.new( :title_link => Link.new(post.name, post_path), :description => post.description, :views => post.view_count, :post_thumbnail => PostThumbnailComponentBuilder.build(post), :comments => post.comments.published.count, :edit_link => Link.new("Edit Post", UrlGenerator.edit_post_path(post)), :status_class => build_status_class(post), :status_text => build_status_text(post), :delete_button => DeleteButtonComponentBuilder.build(post) ) end #... end lib/post_item_component_builder.rb

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class ComponentBuilder def self.build_list(items,*args) return [] if items.nil? or items.empty? if self.respond_to?(:build) items.map do |item| self.build(item,*args) end.compact else raise "ComponentBuilder must implement .build" end end end app/components/component_builder.rb

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class PostItemComponentBuilder < ComponentBuilder def self.build(post) post_path = UrlGenerator.post_path(post) PostItemComponent.new( :title_link => Link.new(post.name, post_path), :description => post.description, :views => post.view_count, :post_thumbnail => PostThumbnailComponentBuilder.build(post), :comments => post.comments.published.count, :edit_link => Link.new("Edit Post", UrlGenerator.edit_post_path(post)), :status_class => build_status_class(post), :status_text => build_status_text(post), :delete_button => DeleteButtonComponentBuilder.build(post) ) end #... end lib/post_item_component_builder.rb

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PostItemComponent = PartialComponent.define( "posts/post_item", :title_link, :description, :views, :comments, :delete_button, :edit_link, :post_thumbnail, :status_class, :status_text) app/components/post_item_component.rb

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class PartialComponent def self.define(partial, *var_names) component_class = ConstructorStruct.new( *[var_names + [:partial]].flatten) component_class.send(:define_method, :locals) do locals = {} var_names.each do |k| locals[k] = instance_variable_get("@#{k}") end locals end component_class.send(:define_method, :render) do |template| template.send(:render, :partial => @partial || partial, :locals => locals) end component_class end end app/components/partial_component.rb

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PostItemComponent = PartialComponent.define( "posts/post_item", :title_link, :description, :views, :comments, :delete_button, :edit_link, :post_thumbnail, :status_class, :status_text) app/components/post_item_component.rb

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.post_item{ :class => status_class } = render_component(post_thumbnail) .text %h5 - if status_text %span= status_text = render_link(title_link) .description= description .stats_and_actions .item_stats %p.views.stat_display %strong.stat_count= views Views %p.comments.stat_display %strong.stat_count= comments Comments .item_actions .edit %a.edit{:href => edit_link.url} %span Edit .delete = render_component(delete_button) app/views/posts/_post_item.html.haml

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Welcome to the team!

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Won’t somebody please think of the new developers?!?!

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View ⬌ Bikeshed

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Typical Summary Example...

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<% published_count = current_user.posts.published.count + current_user.videos.published.count %> <% if published_count > 0 %>
  • Published: <%= published_count %>
    • <% end %> <% draft_count = current_user.posts.unpublished.count + current_user.videos.unpublished.count %> <% if draft_count > 0 %>
  • Drafted: <%= draft_count %>
    • <% end %> app/shared/nav/_author_details.html.erb

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    <% if current_user.admin? %> <% approval_count = current_user.organization.posts.unapproved.count %> <% if approval_count.to_i > 0 %>
  • Needing Approval: <%= approval_count %>
    • <% end %> <% end %> app/shared/nav/_author_details.html.erb (cont)

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    Solutions?

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    class User < ActiveRecord::Base def published_count self.posts.published.count + self.videos.published.count end def draft_count self.posts.unpublished.count + self.videos.unpublished.count end def approval_count if self.admin? self.organization.posts.unapproved.count else 0 end end # ... end app/models/user.rb

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    class AuthorSummary def initialize(author) @author = author end def published_count @author.posts.published.count + @author.videos.published.count end def draft_count @author.posts.unpublished.count + @author.videos.unpublished.count end def approval_count if @author.admin? @author.organization.posts.unapproved.count else 0 end end end lib/author_summary.rb

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    <% summary = AuthorSummary.new(current_user) %> <% if summary.published_count > 0 %>
  • Published: <%= summary.published_count %>
    • <% end %> <% if summary.draft_count > 0 %>
  • Drafted: <%= summary.draft_count %>
    • <% end %> <% if summary.approval_count > 0 %>
  • Needing Approval: <%= summary.approval_count %>
    • <% end %> app/shared/nav/_author_details.html.erb

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    ActiveDecorator github.com/amatsuda/active_decorator

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    module UserDecorator def published_count self.posts.published.count + self.videos.published.count end def draft_count self.posts.unpublished.count + self.videos.unpublished.count end def approval_count if self.admin? self.organization.posts.unapproved.count else 0 end end end app/decorators/user_decorator

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    <% if current_user.published_count > 0 %>
  • Published: <%= current_user.published_count %>
    • <% end %> <% if current_user.draft_count > 0 %>
  • Drafted: <%= current_user.draft_count %>
    • <% end %> <% if current_user.approval_count > 0 %>
  • Needing Approval: <%= current_user.approval_count %>
    • <% end %> app/shared/nav/_author_details.html.erb

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    It helped!

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    Typical Serialization Example...

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    class PostController < ApplicationController before_filter :require_user def show @post = current_organization.posts.find(params[:id]) respond_to do |format| format.html format.json { render :json => @post } end end end app/controllers/posts_controller.rb

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    object @post attributes :id, :title # look up author_name on the model, but use author in the JSON attributes :author_name => :author if current_user.admin? # only show views, popularity to admins attributes :view_count => :views, :popularity_index => :popularity end app/views/posts/show.json.rabl

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    class PostController < ApplicationController before_filter :require_user def show @post = current_organization.posts.find(params[:id]) respond_to do |format| format.html format.json end end end app/controllers/posts_controller.rb

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    class PostSerializer def initialize(post, user) @post, @user = post, user end def to_json if @user && @user.admin? full_detail else summary end end def full_detail summary.merge({ :views => @post.view_count, :popularity => @post.popularity_index }) end def summary { :id => @post.id, :title => @post.title, :author => @post.author_name } end end lib/post_serializer.rb

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    class PostController < ApplicationController before_filter :require_user def show @post = current_organization.posts.find(params[:id]) respond_to do |format| format.html format.json { s = PostSerializer.new(@post, current_user) render :json => s.to_json } end end end app/controllers/posts_controller.rb

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    ActiveModel:: Serializers github.com/josevalim/ active_model_serializers

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    class PostSerializer < ActiveModel::Serializer attributes :id, :title # look up author_name on the model, but use author in the JSON attribute :author_name, :key => :author # @scoped is set to current_user by default if @scoped.admin? attribute :view_count, :key => :views attribute :popularity_index, :key => :popularity end end app/serializers/post_serializer.rb

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    class PostController < ApplicationController before_filter :require_user def show @post = current_organization.posts.find(params[:id]) respond_to do |format| format.html format.json { render :json => @post } end end end app/controllers/posts_controller.rb

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    Pretty cool!

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    But...

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    Is that it?

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    Presenter Definition?

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    Design Patterns

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    Decorator Design Pattern Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

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    Mediator Design Pattern Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently.

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    Presenter Spectrum

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    Presenter Spectrum Models Views Decorators Presenters?

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    Rails: Presenter Pattern blog.jayfields.com/2007/03/rails- presenter-pattern.html

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    Presentation Model martinfowler.com/eaaDev/ PresentationModel.html

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    Presentation Model Presentation Model may interact with several domain objects, but Presentation Model is not a GUI friendly facade to a specific domain object...

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    Presentation Model Instead it is easier to consider Presentation Model as an abstract of the view that is not dependent on a specific GUI framework...

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    Presentation Model While several views can utilize the same Presentation Model, each view should require only one Presentation Model...

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    Presentation Model In the case of composition a Presentation Model may contain one or many child Presentation Model instances, but each child control will also have only one Presentation Model.

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    Definition?

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    “Representation of the State of the View”

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    Presenter == Presentation Model?

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    ViewModel == Presentation Model

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    A Slightly Better Example...

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    <% if @course.available? && @course.self_enrollment && @course.open_enrollment && (!@course_enrollment || !@course_enrollment.active?) && !session["role_course_#{@course.id}"] %> <%= render :partial => "join_course", :object => @course %> <% elsif @course_enrollment && @course_enrollment.self_enrolled && @course_enrollment.active? && (!session["role_course_#{@course.id}"]) %> <%= render :partial => "drop_course", :locals => { :course => @course, :enrollment => @course_enrollment } %> <% elsif temp_type = session["role_course_#{@course.id}"] %> <%= render :partial => "temp_access", :object => temp_type %> <% end %> app/views/course.html.erb

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    <% if @view.show_join_course? %> <%= render :partial => "join_course", :object => @view.course %> <% elsif @view.show_drop_course? %> <%= render :partial => "drop_course", :locals => { :course => @view.course, :enrollment => @view.enrollment } %> <% elsif @view.show_temp_access? %> <%= render :partial => "temp_access", :object => @view.temp_access %> <% end %> app/views/course.html.erb

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    class CourseShowPresenter attr_accessor :course, :enrollment, :user, :session def show_join_course? @course.available? && @course.self_enrollment && @course.open_enrollment && (!@enrollment || !@enrollment.active?) && !show_temp_access? end def show_drop_course? @enrollment && @enrollment.self_enrolled && @enrollment.active? && !show_temp_access? end def show_temp_access? @session["role_course_#{@course.id}"] end alias :temp_access, :show_temp_access? end app/presenters/course_show_presenter.rb

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    class CourseShowPresenter attr_accessor :course, :enrollment, :user, :session def show_join_course? @course.can_user_join?(@user) && !show_temp_access? end def show_drop_course? @course.can_user_drop?(@user) && !show_temp_access? end def show_temp_access? @session["role_course_#{@course.id}"] end alias :temp_access, :show_temp_access? end app/presenters/course_show_presenter.rb

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    <% if @view.show_join_course? %> <%= render :partial => "join_course", :object => @view.course %> <% elsif @view.show_drop_course? %> <%= render :partial => "drop_course", :locals => { :course => @view.course, :enrollment => @view.enrollment } %> <% elsif @view.show_temp_access? %> <%= render :partial => "temp_access", :object => @view.temp_access %> <% end %> app/views/course.html.erb

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    A Good Example...

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    <% if current_organization.feature?(:categories) %> <% if current_site.setting?(:categories) %> <% if user_logged_in? || current_site.setting?(:show_all_content) %> categories = current_site.top_categories <% else %> categories = current_site.top_public_categories <% end %> <% if categories.any? %>
    Top Categories
      <%= render :partial => "category_item", :collection => categories %>
    <% end %> <% end %> <% end %> app/views/home/_sidebar.html.erb

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    class HomepagePresenter attr_accessor :organization, :site, :user # Categories def show_categories? @organization.feature?(:categories) && @site.setting?(:categories) && self.categories.any? end def categories if @user.present? || @site.setting?(:show_all_content) @categories ||= @organization.top_categories else @categories ||= @organization.top_public_categories end end #... end app/presenters/homepage_presenter.rb

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    <% if current_organization.feature?(:categories) %> <% if current_site.setting?(:categories) %> <% if user_logged_in? || current_site.setting?(:show_all_content) %> categories = current_site.top_categories <% else %> categories = current_site.top_public_categories <% end %> <% if categories.any? %>
    Top Categories
      <%= render :partial => "category_item", :collection => categories %>
    <% end %> <% end %> <% end %> app/views/home/_sidebar.html.erb

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    <% if @view.show_categories? %>
    Top Categories
      <%= render :partial => "category_item", :collection => @view.categories %>
    <% end %> app/views/home/_sidebar.html.erb

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    class HomepagePresenter attr_accessor :organization, :site, :user # Categories def show_categories? @organization.feature?(:categories) && @site.setting?(:categories) && self.categories.any? end def categories if @user.present? || @site.setting?(:show_all_content) @categories ||= @organization.top_categories else @categories ||= @organization.top_public_categories end end #... end app/presenters/homepage_presenter.rb

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    class HomepagePresenter #... def categories if show_all_content? @categories ||= @organization.top_categories else @categories ||= @organization.top_public_categories end end protected def show_all_content? @user.present? || @site.setting?(:show_all_content) end #... end app/presenters/homepage_presenter.rb

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    # Presenter when user is logged in class HomepageUserPresenter #... end # Presenter when site shows only public content class HomepagePublicPresenter #... end # Presenter when site shows all content, all the time class HomepagePermissivePresenter #... end app/presenters/homepage_*_presenter.rb

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    class HomepageController < ApplicationController def index @view = build_homepage_presenter respond_to do |format| format.html end end def build_homepage_presenter view = if user_logged_in? HomepageUserPresenter.new elsif current_site.setting?(:show_all_content) HomepagePermissivePresenter.new else HomepagePublicPresenter.new end view.organization = current_organization view.site = current_site view.user = current_user view end end app/controllers/homepage_controller.rb

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    Warning!

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    Thank you!

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    HIRE ME!!! blowmage.com Questions?