Fixes #1230. Makes comment counter more efficient

db/migrate/20170316042351_add_comment_count_to_events.rb

@@ -0,0 +1,15 @@
+class AddCommentCountToEvents < ActiveRecord::Migration
+  def up
+    add_column :events, :comments_count, :integer, default: 0
+
+    Event.reset_column_information
+
+    Event.find_each do |event|
+      event.update_attribute :comments_count, event.comment_threads.length
+    end
+  end
+
+  def down
+    remove_column :events, :comments_count
+  end
+end