gistfile1.rb

#schema.rb

ActiveRecord::Schema.define(:version => 2) do
  create_table "stories", :force => true do |t|
    t.string "title", "subtitle"
    t.string  "type"
    t.integer "length_counter", :default => 0
    t.boolean "published"
  end

  create_table "characters", :force => true do |t|
    t.integer "story_id"
    t.string "name"
  end
end

#spec_helper.rb
    Character.class_eval do
      index [:name, :story_id]
      index [:id, :story_id]
      index [:id, :name, :story_id]

      belongs_to :story

      def after_create
        story.increment(:length_counter, self.name.length) if self.name && story
      end
    end

#spec code
        it 'increments the count in callback' do
          story = Story.create!(:title => 'story')
          story.length_counter.should == 0

          character = story.characters.create!(:name => "character")
          story.length_counter.should == character.name.length
        end