redis:- session key not updating

问题

redisClient.set('sessionKey', userSession, function(err){
 console.log(err || 'sessionKey updated');
});

The above works.

But following does not update the existing session key.

redisClient.get(sessionKey, function(err, userSession){ // works fine
    userSession = // some modification;
    redisClient.set(sessionKey, userSession, function(err){
      console.log(err || 'sessionKey updated');
    });
 });

I'm using localhost with redistogo thru heroku. There is no error. Even the console.log(err || 'sessionkey update'); prints

来源：https://stackoverflow.com/questions/20331355/redis-session-key-not-updating