Only include quiz question_types in api responses

The Quiz#question_types method is expensive for large quizzes. It's
currently called every time a quiz is serialized, even though we only
need the question_types attribute in API responses (I believe it's used
by the mobile app).

This commit moves the question_types attribute to a separate
QuizApiSerializer that is only used in API responses.

Fixes QO-356
Fixes QO-357

Test plan:

- Create several huge quizzes (tens of thousands of questions across
  multiple question groups)
- Open the quizzes list page
- Check that the page loads reasonably quickly

Change-Id: Id18a32fc47f20cd24cb178e972f49e8984bfe53e
Reviewed-on: https://gerrit.instructure.com/149829
Reviewed-by: James Williams  <jamesw@instructure.com>
Tested-by: Jenkins
QA-Review: David Tan <dtan@instructure.com>
Product-Review: Omar Khan <okhan@instructure.com>

app/serializers/quizzes/quiz_api_serializer.rb

@@ -0,0 +1,26 @@
+#
+# Copyright (C) 2018 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+module Quizzes
+  class QuizApiSerializer < QuizSerializer
+    # The Quiz#question_types method is expensive to call for large quizzes.
+    # Splitting it out into a separate serializer allows us to include it only
+    # where needed (the API).
+    attributes :question_types
+  end
+end

app/serializers/quizzes/quiz_serializer.rb

@@ -39,7 +39,7 @@ module Quizzes
                 :quiz_submissions_zip_url, :preview_url, :quiz_submission_versions_html_url,
                 :assignment_id, :one_time_results, :only_visible_to_overrides,
                 :assignment_group_id, :show_correct_answers_last_attempt, :version_number,
-                :question_types, :has_access_code, :post_to_sis, :anonymous_submissions
+                :has_access_code, :post_to_sis, :anonymous_submissions
 
     def_delegators :@controller,
       # :api_v1_course_assignment_group_url,

lib/api/v1/quiz.rb

@@ -71,7 +71,7 @@ module Api::V1::Quiz
                          scope: user,
                          session: session,
                          root: :quizzes,
-                         each_serializer: Quizzes::QuizSerializer,
+                         each_serializer: Quizzes::QuizApiSerializer,
                          controller: self,
                          serializer_options: options).as_json
     else

spec/apis/v1/quizzes/quizzes_api_spec.rb

@@ -234,7 +234,7 @@ describe Quizzes::QuizzesApiController, type: :request do
                         'Accept' => 'application/vnd.api+json')
         @json = @json.fetch('quizzes').map { |q| q.with_indifferent_access }
         expect(@json).to match_array [
-          Quizzes::QuizSerializer.new(@quiz, scope: @user, controller: controller, session: session).
+          Quizzes::QuizApiSerializer.new(@quiz, scope: @user, controller: controller, session: session).
           as_json[:quiz].with_indifferent_access
         ]
       end
@@ -272,7 +272,7 @@ describe Quizzes::QuizzesApiController, type: :request do
         @course.reload
         @quiz = @course.quizzes.first
         expect(@json).to match_array [
-          Quizzes::QuizSerializer.new(@quiz, scope: @user, controller: controller, session: session).
+          Quizzes::QuizApiSerializer.new(@quiz, scope: @user, controller: controller, session: session).
           as_json[:quiz].with_indifferent_access
         ]
       end

spec/serializers/quizzes/quiz_api_serializer_spec.rb

@@ -0,0 +1,25 @@
+#
+# Copyright (C) 2018 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+require 'spec_helper'
+
+describe Quizzes::QuizApiSerializer do
+  it 'includes question_types' do
+    expect(described_class._attributes).to include(:question_types)
+  end
+end

spec/serializers/quizzes/quiz_serializer_spec.rb

@@ -60,7 +60,7 @@ describe Quizzes::QuizSerializer do
     :allowed_attempts, :one_question_at_a_time, :question_count,
     :points_possible, :cant_go_back, :access_code, :ip_filter, :due_at,
     :lock_at, :unlock_at, :published, :show_correct_answers_at,
-    :hide_correct_answers_at, :show_correct_answers_last_attempt, :question_types,
+    :hide_correct_answers_at, :show_correct_answers_last_attempt,
     :has_access_code
   ].each do |attribute|
 
@@ -625,4 +625,8 @@ describe Quizzes::QuizSerializer do
     new_json = quiz_serializer.as_json[:quiz]
     expect(new_json[:anonymous_submissions]).to eq true
   end
+
+  it "does not include question_types" do
+    expect(json.keys).not_to include(:question_types)
+  end
 end