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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)

· Database Zone ·
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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

Compliant Database DevOps and the role of DevSecOps DevOps is becoming the new normal in application development, and DevSecOps is now entering the picture. By balancing the desire to release code faster with the need for the same code to be secure, it addresses increasing demands for data privacy. But what about the database? How can databases be included in both DevOps and DevSecOps? What additional measures should be considered to achieve truly compliant database DevOps? This whitepaper provides a valuable insight. Get the whitepaper

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