Add decorates_assigned method to controllers

lib/draper.rb

@@ -21,6 +21,7 @@ require 'draper/decorated_association'
 require 'draper/helper_support'
 require 'draper/view_context'
 require 'draper/collection_decorator'
+require 'draper/decorates_assigned'
 require 'draper/railtie' if defined?(Rails)
 
 module Draper
@@ -28,6 +29,7 @@ module Draper
     base.class_eval do
       include Draper::ViewContext
       extend  Draper::HelperSupport
+      extend  Draper::DecoratesAssigned
 
       before_filter do |controller|
         Draper::ViewContext.clear!

lib/draper/decorates_assigned.rb

@@ -0,0 +1,39 @@
+module Draper
+  module DecoratesAssigned
+    # @overload decorates_assigned(*variables, options = {})
+    #   Defines a helper method to access decorated instance variables.
+    #
+    #   @example
+    #     # app/controllers/articles_controller.rb
+    #     class ArticlesController < ApplicationController
+    #       decorates_assigned :article
+    #
+    #       def show
+    #         @article = Article.find(params[:id])
+    #       end
+    #     end
+    #
+    #     # app/views/articles/show.html.erb
+    #     <%= article.decorated_title %>
+    #
+    #   @param [Symbols*] variables
+    #     names of the instance variables to decorate (without the `@`).
+    #   @param [Hash] options
+    #     see {Factory#initialize}
+    def decorates_assigned(*variables)
+      factory = Draper::Factory.new(variables.extract_options!)
+
+      variables.each do |variable|
+        undecorated = "@#{variable}"
+        decorated = "@decorated_#{variable}"
+
+        define_method variable do
+          return instance_variable_get(decorated) if instance_variable_defined?(decorated)
+          instance_variable_set decorated, factory.decorate(instance_variable_get(undecorated))
+        end
+
+        helper_method variable
+      end
+    end
+  end
+end

spec/draper/decorates_assigned_spec.rb

@@ -0,0 +1,71 @@
+require 'spec_helper'
+
+module Draper
+  describe DecoratesAssigned do
+    let(:controller_class) do
+      Class.new do
+        extend DecoratesAssigned
+
+        def self.helper_method(method)
+          helper_methods << method
+        end
+
+        def self.helper_methods
+          @helper_methods ||= []
+        end
+      end
+    end
+
+    describe ".decorates_assigned" do
+      it "adds helper methods" do
+        controller_class.decorates_assigned :article, :author
+
+        expect(controller_class.instance_methods).to include :article
+        expect(controller_class.instance_methods).to include :author
+
+        expect(controller_class.helper_methods).to include :article
+        expect(controller_class.helper_methods).to include :author
+      end
+
+      it "creates a factory" do
+        Factory.should_receive(:new).once
+        controller_class.decorates_assigned :article, :author
+      end
+
+      it "passes options to the factory" do
+        options = {foo: "bar"}
+
+        Factory.should_receive(:new).with(options)
+        controller_class.decorates_assigned :article, :author, options
+      end
+
+      describe "the generated method" do
+        it "decorates the instance variable" do
+          source = double
+          factory = double
+          Factory.stub new: factory
+
+          controller_class.decorates_assigned :article
+          controller = controller_class.new
+          controller.instance_variable_set "@article", source
+
+          factory.should_receive(:decorate).with(source).and_return(:decorated)
+          expect(controller.article).to be :decorated
+        end
+
+        it "memoizes" do
+          factory = double
+          Factory.stub new: factory
+
+          controller_class.decorates_assigned :article
+          controller = controller_class.new
+
+          factory.should_receive(:decorate).once
+          controller.article
+          controller.article
+        end
+      end
+    end
+
+  end
+end

spec/dummy/app/controllers/posts_controller.rb

@@ -1,6 +1,8 @@
 class PostsController < ApplicationController
+  decorates_assigned :post
+
   def show
-    @post = Post.find(params[:id]).decorate
+    @post = Post.find(params[:id])
   end
 
   def mail

spec/dummy/app/views/posts/show.html.erb

@@ -1 +1 @@
-<%= render @post %>
+<%= render post %>