def from_file(filename)
      unless File.exist?(filename)
        raise DirCatException.new, "'#{filename}' not exists"
      end
      dircat_ser = File.open(filename) { |f| YAML::load(f) }
      @dirname = dircat_ser.dirname
      @ctime = dircat_ser.ctime
      dircat_ser.entries.each do |entry_ser|
        add_entry(Entry.from_ser(entry_ser))
      end
      self
    end
def from_file(filename)
      unless File.exist?(filename)
        raise DirCatException.new, "'#{filename}' not exists"
      end
      dircat_ser = File.open(filename) { |f| YAML::load(f) }
      @dirname = dircat_ser.dirname
      @ctime = dircat_ser.ctime
      dircat_ser.entries.each do |entry_ser|
        add_entry(Entry.from_ser(entry_ser))
      end
      self
    end
Load catalog from a file