caching comment counts

db/migrate/20161229080315_add_comments_count_to_events.rb

@@ -0,0 +1,10 @@
+class AddCommentsCountToEvents < ActiveRecord::Migration
+  def change
+    add_column :events, :comments_count, :integer, default: 0, null: false
+
+    Event.find_each do |event|
+      comments_count = event.comment_threads.count
+      event.update_attribute(:comments_count, comments_count) unless comments_count.zero?
+    end
+  end
+end

db/schema.rb

@@ -242,6 +242,7 @@ ActiveRecord::Schema.define(version: 20170629232817) do
     t.boolean  "is_highlight",                 default: false
     t.integer  "program_id"
     t.integer  "max_attendees"
+    t.integer  "comments_count",               default: 0,     null: false
   end
 
   create_table "events_registrations", force: :cascade do |t|