CODEWITHSUNDEEP
node.jsasynchronousredis
proquibas
proquibas

Reputation: 91

Node.js & Redis get key data

I read a lot about this problem but I can't solve it. I'm working in a code in node.js and redis to get the data from a key. Of course, when I execute client.get it prints data as nul or undefined because of async. But I don't know how to solve it.

Example code: this part works fine

     pubsub.on('psubscribe', function() {
            while(i<end){
                client.set( i , url, function() {
                });
                client.expire( i , 10);
                   console.log("New key: " + i);
                i++;
                }
    });

Then, when the key expires I want to get de data to set it again in Redis:

    pubsub.on('pmessage', function(channel, message) {
        var keyData;
        client.get(message, function(err,data){
          keyData = data;
        });
        client.set( message , keyData, function(){});
        client.expire( message , 10);

    });

Of course, data is null.

How can I solve it?

Thanks a lot.

Upvotes: 0

Views: 8134

Answers (1)

georoot
georoot

Reputation: 3617

The issue is because node is async in nature. Here is something that might help you out.

client.get(message,(err,data)=>{
  client.set( message , data,()=>{
    client.expire( message , 10);
  });
});

This being said, it is a bad implementation and would lead to callback hell. A better implementation using promise would be

var clientGet = (message)=>{
  return new Promise((fullfill,reject)=>{
    client.get(message,(err,data)=>{
      if(err)
        reject(err);
      else
        fullfill([message,data]);
    });
  });
}


var clientSet = (dataFromGet)=>{
  return new Promise((fullfill,reject)=>{
    let message,data = dataFromGet;
    client.set(message,data,()=>{
      fullfill(message);
    });
  });
}


var clientExpire = (message)=>{
  return new Promise((fullfill,reject)=>{
    client.expire(message,10);
    fullfill();
  });
}

And you can call them using

clientGet(message)
  .then(clientSet)
  .then(clientExpire)
  .then(()=>{
    console.log("All operations were fine");
  })
  .catch((ex)=>{
    console.err(ex.message);
  });

Why not to use first method

As i wrote previously it would lead to callback hell which is basically a lot of callbacks inside one another. As you can see from the first part of the code that there were two functions, they might increase and usually makes the code more difficult to manage and read.

Upvotes: 2

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