# File lib/dragonfly/data_storage/mongo_data_store.rb, line 46
      def retrieve(uid)
        ensure_authenticated!
        grid_io = grid.get(bson_id(uid))
        meta = marshal_decode(grid_io.metadata)
        meta.merge!(:stored_at => grid_io.upload_date)
        [
          grid_io.read,
          meta
        ]
      rescue Mongo::GridFileNotFound, INVALID_OBJECT_ID => e
        raise DataNotFound, "#{e} - #{uid}"
      end