Redis in NodeJS

For each query on a server, it is not ideal to fetch data directly from the database because we may or may not have an Index for that type of query in the DB which may cause the full-scan of the db in the worst case.

So, we need to have some sort of server that will cache the responses for a type of query so that next time, the same query is requested, we can return the cached response.

Redis is a in-memory, key-value store which is mostly used for caching. In this post, we will see, how we can use Redis in a Node application.

Prerequisites

• Install Node (either by NVM or global installation)
• Install and setup Docker.

Installing Redis

Installing redis is not the same for all platforms. So, we are going to use docker to run redis on our machine.

$ docker run -d -p 6379:6379 --name some-redis redis  

This will start up the Redis server on port $6379$.

Installing Redis package to interact with the Redis server

$ npm install redis  

Using Redis in the application

• Storing and Retrieving values

const redis = require("redis");  
  
// Redis connection string  
const redisUrl = process.env.REDIS_URL || `redis://localhost:6379`;  
// In production, set the "REDIS_URL" environment variable for the redis server.  
  
// Create a connection  
const client = redis.createClient(redisUrl);  
  
client.on("connect", () => {  
  main();
});  
  
const main = () => {  
  // Setting a value 
  client.set("hi", "there", redis.print);  
  
  // To get the value 
  client.get("hi", (err, value) => { 
    if (err) { 
	  console.log(err); return; 
	} 
	console.log(value); 
  });
};  

* Using hashes

const express = require("express");  
const redis = require("redis");  
  
// Redis connection string  
const redisUrl = process.env.REDIS_URL || `redis://localhost:6379`;  
// In production, set the "REDIS_URL" environment variable for the redis server.  
  
// Create a connection  
const client = redis.createClient(redisUrl);  
  
client.on("connect", () => {  
  main();
});  
  
const main = () => {  
 // Hash set 
 // For "user" hash, the following sets 2 properties ["name", "website"].  
 // You can set multiple key-values (Up to 3 pairs, max, I guess).  
 client.hset("user", "name", "vighnesh", "website", "https://vighnesh153.com");  
 
 client.hget("user", "name", redis.print); 
 // Reply: vighnesh  
 
 client.hgetall("user", (err, val) => { 
   if (err) {
     console.log(err); 
     return;
   } 
   console.log(val); 
 }); 
 // { name: 'vighnesh', website: 'https://vighnesh153.com' }};  

* Storing JS objects

const express = require("express");  
const redis = require("redis");  
  
// Redis connection string  
const redisUrl = process.env.REDIS_URL || `redis://localhost:6379`;  
// In production, set the "REDIS_URL" environment variable for the redis server.  
  
// Create a connection  
const client = redis.createClient(redisUrl);  
  
client.on("connect", () => {  
  main();
});  
  
const main = () => {  
 // Storing object: We can only store strings or numbers in Redis store. 
  client.set("me", JSON.stringify({ 
    name: "Vighnesh", 
    birthYear: "1998" 
  }))  
  
  client.get("me", (err, value) => { 
    if (err) {
      console.log(err); 
      return;
    } 
    const me = JSON.parse(value);  
    console.log(me); 
    // { name: 'Vighnesh', birthYear: '1998' }};
  });  

Cache Timeout or Expiry

client.set("name", "vighnesh", "EX", 5);  // 5 seconds  
  
// For 5 seconds, `client.get("name")` will resolve to "vighnesh", // and after 5 seconds, it will resolve to `null`.  

Clear cache

// Clear a specific hash  
client.del("key");  
  
// Clear entire cache  
client.flushall();  

Sample express app using Redis

const util = require("util");  
  
const express = require("express");  
const app = express();  
  
const redis = require("redis");  
const redisUrl = process.env.REDIS_URL || `redis://localhost:6379`;  
const client = redis.createClient(redisUrl);  
client.get = util.promisify(client.get);  
  
  
app.get("/", async (req, res) => {  
  const numbers = await client.get("numbers"); 
  if (numbers) { 
    return res.json(JSON.parse(numbers)); 
  }  
 
  // Simulate a delay of 5 seconds 
  setTimeout(() => { 
    const numbers = [1, 2, 3, 4, 5]; 
    res.json(numbers); 
    client.set("numbers", JSON.stringify(numbers)); 
  }, 5000);
  
});  
  
  
app.listen(4200, () => {  
  console.log(`Listening on http://localhost:4200`);
});  

I hope this post helped you to understand how to use redis in a node application. Feel free to share your thoughts in the comments section below.