json.cache! [@exercise, @exercise.topic] do
  json.topic do |topic|
    topic.num   @exercise.topic.num
    topic.title @exercise.topic.title
  end
  json.exercise_id @exercise.id
  json.color       @exercise.color
  json.rep_num     @exercise.rep_num
  json.features    @exercise.topic.features.split(' ')
  json.json        @exercise.json_loaded
  json.paths do |paths|
    paths.next_exercise @exercise.path_for_next_exercise
    paths.next_rep      @exercise.path_for_next_rep
  end
end
