docs: function updateSnapshot(app, uid, cb) {
    logger.debug('updateSnapshot entry');
  
    app.models.snapshot.findOne(
      { where: { current: 'true' } },
      function(err, instance) {
        if (err) {
          // fall through assuming there was no current
        } else if (instance) {
          instance.updateAttributes(
            { current: 'false' },
            function(err, instance) {
              if (err) {
                // fall through assuming instance was deleted
              }
            });
          releaseSnapshot(app, instance.id);
        }
      });
  
    app.models.snapshot.findById(uid, function(err, instance) {
      if (err) {
        logger.debug('updateSnapshot error(1)');
        cb(err);
        return;
      }
  
      instance.updateAttributes(
        { current: 'true' },
        function(err, instance) {
          if (err) {
            logger.debug('updateSnapshot error(2)');
            cb(err);
            return;
          }
          logger.debug('updateSnapshot exit');
          cb();
        });
    });
  }