# File lib/rgen/fragment/fragmented_model.rb, line 113
  def index
    fragments.each do |f|
      if !@fragment_index[f] || (@fragment_index[f].object_id != f.index.object_id)
        @fragment_index[f] = f.index
        invalidate_cache
      end
    end
    return @index if @index
    @index = {}
    fragments.each do |f|
      f.index.each do |i| 
        (@index[i[0]] ||= []) << i[1]
      end
    end
    @index
  end