def add(object)
      key, id = to_key_and_id(object)

      @graph[key] ? @graph[key] << id : @graph[key] = [id]
    end
def add(object)
      key, id = to_key_and_id(object)

      @graph[key] ? @graph[key] << id : @graph[key] = [id]
    end
Add this object to the object tracker.