Async NodeJS request to Redis db

Question

I need to do several request to Redis db, and I need the response from a request to do the next one.

Let's analyze this example: (I'm using node_redis for the requests)

var message-id = undefined;

// request the next id
client.incr("message-id", function(err, id) {
    message-id = id;
});

// use the 'next id' for storing a message
client.hmset("messages", message-id, messageContent);

This way doesn't work, because message-id id still undefined when I call client.hmdet().

The following is the lazy way, and it consist in put the client.hmdet() inside the client.incr() callback. var message-id = undefined;

// request the next id
client.incr("message-id", function(err, id) {
    message-id = id;

    // use the 'next id' for storing a message
    client.hmset("messages", message-id, messageContent, function(){
        //more request here
    });
});

I think this is not a good way to proceed, because if I have lots chained request, I need to put each request inside its previous request callback, and this will create a block of code hard to maintain.

I'm interested in the best practices for doing lots of request asynchronously. Can someone advise me?

you'r missing a closing ) in line 6 of the first code block

alfonsodev
– alfonsodev

2013-12-06 11:19:37 +00:00
Commented Dec 6, 2013 at 11:19 — alfonsodev
– alfonsodev, Commented Dec 6, 2013 at 11:19

alfonsodev · Accepted Answer · 2013-12-06 11:15:27Z

1

I recommend you to have a look to the async module, it implements several patterns that you can use. your example async waterfall

async.waterfall([
    function(callback){
        callback(null, 'one', 'two');
    },
    function(arg1, arg2, callback){
        callback(null, 'three');
    },
    function(arg1, callback){
        // arg1 now equals 'three'
        callback(null, 'done');
    }
], function (err, result) {
   // result now equals 'done'    
});

And also if you want to explore other possibilities beyond the callback pattern, you have the q module that implements promises A+

answered Dec 6, 2013 at 11:15

alfonsodev

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3 Comments

RikyTres Over a year ago

Thanks! Q module is really interesting!

RikyTres Over a year ago

Anyway, I think that could be really useful if any redis method has a flag for set the request as sync ora async... ;)

RikyTres Over a year ago

I really don't understand how to do this with promises A+ way... I't not explained well in my opinion... -_-'

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