Replace Subclasses with Strategies: Step Eight

* Introduce polymorphic association for strategy
* Build the strategy when building the root type

Author: jferris

example_app/app/controllers/questions_controller.rb

@@ -32,6 +32,7 @@ def update
 
   def build_question
     @question = type.constantize.new(question_params)
+    @question.build_submittable
     @question.survey = @survey
   end
 

example_app/app/models/question.rb

@@ -6,6 +6,7 @@ class Question < ActiveRecord::Base
   validates :type, presence: true, inclusion: QUESTION_TYPES
   validates :title, presence: true
 
+  belongs_to :submittable, polymorphic: true
   belongs_to :survey
   has_many :answers
 
@@ -16,9 +17,9 @@ def most_recent_answer_text
     answers.most_recent.text
   end
 
-  def submittable
+  def build_submittable
     submittable_class = type.sub('Question', 'Submittable').constantize
-    submittable_class.new(question: self)
+    self.submittable = submittable_class.new(question: self)
   end
 
   def summarize(summarizer)
@@ -30,6 +31,7 @@ def switch_to(type, new_attributes)
     attributes = self.attributes.merge(new_attributes)
     cloned_attributes = attributes.except('id', 'type', 'submittable_type')
     new_question = type.constantize.new(cloned_attributes)
+    new_question.build_submittable
     new_question.id = id
 
     begin

example_app/db/migrate/20130131203344_add_submittable_type_and_id_to_questions.rb

@@ -0,0 +1,6 @@
+class AddSubmittableTypeAndIdToQuestions < ActiveRecord::Migration
+  def change
+    add_column :questions, :submittable_id, :integer
+    add_column :questions, :submittable_type, :string
+  end
+end

example_app/db/schema.rb

@@ -67,13 +67,15 @@
   end
 
   create_table "questions", :force => true do |t|
-    t.string   "title",      :null => false
-    t.string   "type",       :null => false
-    t.integer  "survey_id",  :null => false
-    t.datetime "created_at", :null => false
-    t.datetime "updated_at", :null => false
+    t.string   "title",            :null => false
+    t.string   "type",             :null => false
+    t.integer  "survey_id",        :null => false
+    t.datetime "created_at",       :null => false
+    t.datetime "updated_at",       :null => false
     t.integer  "minimum"
     t.integer  "maximum"
+    t.integer  "submittable_id"
+    t.string   "submittable_type"
   end
 
   create_table "scale_submittables", :force => true do |t|

example_app/spec/factories/application.rb

@@ -10,6 +10,12 @@
     user
   end
 
+  factory :multiple_choice_submittable do
+  end
+
+  factory :open_submittable do
+  end
+
   factory :option do
     text 'Hello'
   end
@@ -28,17 +34,25 @@
           FactoryGirl.build(:option, text: text, question_id: attributes.id)
         end
       end
+
+      submittable factory: :multiple_choice_submittable
     end
 
     factory :open_question, class: 'OpenQuestion' do
+      submittable factory: :open_submittable
     end
 
     factory :scale_question, class: 'ScaleQuestion' do
       minimum 1
       maximum 2
+
+      submittable factory: :scale_submittable
     end
   end
 
+  factory :scale_submittable do
+  end
+
   factory :survey do
     sequence(:title) { |n| "Survey #{n}" }
     author factory: :user

example_app/spec/models/question_spec.rb

@@ -11,10 +11,21 @@
 
   it { should validate_presence_of :title }
 
+  it { should belong_to(:submittable) }
   it { should belong_to(:survey) }
   it { should have_many(:answers) }
 end
 
+describe Question, '#build_submittable' do
+  it 'builds a submittable with its type' do
+    question = build(:open_question)
+
+    question.build_submittable
+
+    question.submittable.should be_a(OpenSubmittable)
+  end
+end
+
 describe Question, '#most_recent_answer_text' do
   it 'returns the text for the latest answer' do
     question = create(:open_question)
@@ -36,13 +47,6 @@
   end
 end
 
-describe Question, '#submittable' do
-  it 'instantiates a submittable based on its type' do
-    question = create(:open_question)
-    question.submittable.should be_a(OpenSubmittable)
-  end
-end
-
 describe Question, '#summarize' do
   it 'builds a summary with the result from the summarizer' do
     question = build_stubbed(:question)