zammad/app/models/observer/ticket/article_counter.rb

# Copyright (C) 2012-2014 Zammad Foundation, http://zammad-foundation.org/

class Observer::Ticket::ArticleCounter < ActiveRecord::Observer
  observe 'ticket::_article'

  def after_create(record)

    # get article count
    record.ticket.article_count = record.ticket.articles.count

    # save ticket
    record.ticket.save
  end
end