Redis basic

Installing redis server.

1. Ubuntu based system.

   • sudo apt update
   • sudo apt install redis
   • sudo systemctl start redis
   • redis-cli ping

2. Centos/RHEAL based system

   • Digital Ocean Reference
   • sudo yum install epel-release
   • sudo yum install redis -y
   • systemctl start redis.service
   • redis-cli ping

• after running redis-cli ping you will get PONG in return from the server

Connecting Javascript project to redis.

• to connect our javascript to redis, we use redis node module.
• install redis using: npm install redis.
• then you can require the module using: const redis = require('redis')
• default redis url for redis server in localhost : redis://127.0.0.1:6379
• example code to create connection to server.

    const redis  = require('redis');
    const redisUrl = 'redis://127.0.0.1:6379'; 
    const client = redis.createClient(redisUrl);

Storing and Getting Data to Redis

• redis store data in form of (key,value) index.
• we can only store string data in redis, so let say you want to store an object or array you need to stringify it into a json object.
• to store data in redis, we use the set method from the redis node module.
• example code.

    client.set('myKey','myValue',myCallback);

• to get data from redis, we use get method by giving the key as the parameter
• example code.

    client.get('myKey',myCallback)

• the callback for get method returns two value, error and value of the key.
• so let say we simply want to print the value.

    //this will print the value 'myValue` we previously set.
    client.get('myKey',(error,value)=>console.log(value)); 

• noticed that we are require to pass a callback in order to receive data from server, because this is an asynchronous operation.
• if you don't want to use callback and instead want to use promise, we can make use of promisify to convert our function into returning a promise.

    const {promisify} = require('util');
    const getAsync = promisify(client.get).bind(client);    

• getAsync is now our new function that will return a promise
• we can use it with await or using then
• example using await.

    //make sure this code run in async function
    try{
        const value = await getAsync('myKey');
        console.log(value);
    }catch(error){
        console.error(error)
    }

• example using .then

    getAsync('myKey').then(console.log).catch(console.error)