# File lib/moneta/adapters/mongo.rb, line 63
      def load(key, options = {})
        key = to_binary(key)
        doc = @collection.find_one('_id' => key)
        if doc && (!doc[@expires_field] || doc[@expires_field] >= Time.now)
          expires = expires_at(options, nil)
          @collection.update({ '_id' => key },
                             # @expires_field must be a Time object (BSON date datatype)
                             { '$set' => { @expires_field => expires || nil } }) if expires != nil
          doc_to_value(doc)
        end
      end