def upgrade_file_key(key, save = true)
      cname = self.collection.name

      files = self.database["#{cname}.files"]
      chunks = self.database["#{cname}.chunks"]

      fname = self["_#{key}"] rescue nil
      return if fname.blank?

      begin
        n = Mongo::GridIO.new(files, chunks, fname, "r", :query => {:filename => fname})

        v = n.read

        if !v.empty?
          data = StringIO.new(v)
          self.put_file(key, data)
          self["_#{key}"] = nil

          self.save(:validate => false) if save
        end
      rescue => e
        puts "ERROR: #{e}"
        puts e.backtrace.join("\t\n")
        return
      end

      files.remove(:_id => fname)
      chunks.remove(:_id => fname)
    end
def upgrade_file_key(key, save = true)
      cname = self.collection.name

      files = self.database["#{cname}.files"]
      chunks = self.database["#{cname}.chunks"]

      fname = self["_#{key}"] rescue nil
      return if fname.blank?

      begin
        n = Mongo::GridIO.new(files, chunks, fname, "r", :query => {:filename => fname})

        v = n.read

        if !v.empty?
          data = StringIO.new(v)
          self.put_file(key, data)
          self["_#{key}"] = nil

          self.save(:validate => false) if save
        end
      rescue => e
        puts "ERROR: #{e}"
        puts e.backtrace.join("\t\n")
        return
      end

      files.remove(:_id => fname)
      chunks.remove(:_id => fname)
    end
NOTE: this method will be removed on next release