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Tutorial: Working with Node.js and Redis (Expire and TTL)

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Tutorial: Working with Node.js and Redis (Expire and TTL)

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In my previous post I showed you how to install and use Redis with Node.js. Today I’m going to take that a step further and walk through some of the things you can do with node_redis using Redis’s TTL and EXPIRE commands.

Note: If you haven’t gone through my previous article make sure to do that now as I’ll assume you have Node.js and Redis up and running.

Create a new folder and put a new text file in it called: app.js

Inside the app.js file we will add some simple code to set a value that doesn’t have a time to live (or expiration on it):

var redis = require("redis")
    , client = redis.createClient();
 
client.on("error", function (err) {
    console.log("Error " + err);
});
 
client.on("connect", runSample);
 
function runSample() {
    // Set a value
    client.set("string key", "Hello World", function (err, reply) {
        console.log(reply.toString());
    });
    // Get a value
    client.get("string key", function (err, reply) {
        console.log(reply.toString());
    });
}

When we connect to Redis and everything is ready the runSample function is called which in turn sets a value and then reads it back.

Expected output:

OK
Hello World

Lets set a timeout on a value using the EXPIRE command and see what happens. Replace the original code with this:

var redis = require('redis')
    , client = redis.createClient();
 
client.on('error', function (err) {
    console.log('Error ' + err);
});
 
client.on('connect', runSample);
 
function runSample() {
    // Set a value with an expiration
    client.set('string key', 'Hello World', redis.print);
    // Expire in 3 seconds
    client.expire('string key', 3);
 
    // This timer is only to demo the TTL
    // Runs every second until the timeout
    // occurs on the value
    var myTimer = setInterval(function() {
        client.get('string key', function (err, reply) {
            if(reply) {
                console.log('I live: ' + reply.toString());
            } else {
                clearTimeout(myTimer);
                console.log('I expired');
                client.quit();
            }
        });
    }, 1000);
}

Note: Be aware that the timer I use is just to demo the EXPIRE, you should be very careful about using timers in production Nodejs projects.

Run the program. Expected results:

Reply: OK
I live: Hello World
I live: Hello World
I live: Hello World
I expired

Now we will check to see how much time a value has left before it expires:

var redis = require('redis')
    , client = redis.createClient();
 
client.on('error', function (err) {
    console.log('Error ' + err);
});
 
client.on('connect', runSample);
 
function runSample() {
    // Set a value
    client.set('string key', 'Hello World', redis.print);
    // Expire in 3 seconds
    client.expire('string key', 3);
 
    // This timer is only to demo the TTL
    // Runs every second until the timeout
    // occurs on the value
    var myTimer = setInterval(function() {
        client.get('string key', function (err, reply) {
            if(reply) {
                console.log('I live: ' + reply.toString());
                client.ttl('string key', writeTTL);
            } else {
                clearTimeout(myTimer);
                console.log('I expired');
                client.quit();
            }
        });
    }, 1000);
}
 
function writeTTL(err, data) {
    console.log('I live for this long yet: ' + data);
}

Run the program. Expected results:

Reply: OK
I live: Hello World
I live for this long yet: 2
I live: Hello World
I live for this long yet: 1
I live: Hello World
I live for this long yet: 0
I expired

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