PERF: tag groups index query

app/controllers/tag_groups_controller.rb

@@ -4,7 +4,7 @@ class TagGroupsController < ApplicationController
   before_filter :fetch_tag_group, only: [:show, :update, :destroy]
 
   def index
-    tag_groups = TagGroup.order('name ASC').includes(:parent_tag).all
+    tag_groups = TagGroup.order('name ASC').includes(:parent_tag).preload(:tags).all
     serializer = ActiveModel::ArraySerializer.new(tag_groups, each_serializer: TagGroupSerializer, root: 'tag_groups')
     respond_to do |format|
       format.html do

app/serializers/tag_group_serializer.rb

@@ -2,7 +2,7 @@ class TagGroupSerializer < ApplicationSerializer
   attributes :id, :name, :tag_names, :parent_tag_name, :one_per_topic
 
   def tag_names
-    object.tags.pluck(:name).sort
+    object.tags.map(&:name).sort
   end
 
   def parent_tag_name