node.js, domino-db & Docker (6): Using memcached

mem.js

I am using mem.js as client library for accessing memcached. To use it, the first thing to do is to add the requirement to your package.json:

npm install memjs --save

MemcachedFactory

Then we can create a simple helper class to have an abstraction layer between our code and the library itself.

1. Create a folder in /app named classes

2. Create a new file with the name MemcachedFactory.js

3. Add the following code:

const memjs = require('memjs');
/**
 * Helper class for using Memcache
 * 
 * @author Sven Hasselbach
 * @version 0.1
 */
class MemcachedFactory {

    constructor() {
      this.client = memjs.Client.create('127.0.0.1:11211');
    }

    /**
     * returns a single instance of the class
     */
    static getInstance() {
      if (this.instance == null) {
        this.instance = new MemcachedFactory();
      }
      return this.instance;
    }

    /**
     * stores a value in memcache
     * @param {string} key 
     *  the key used
     * @param {*} value
     *  the value to store
     * @param {number} ttl 
     *  time-to-live in seconds
     */
    set(key, value, ttl) {
      this.client.set(key, value, { expires: ttl }, err => {
        if (err) {
          console.log(err);
          throw err;
        }
      });
    }
    /**
     * gets a value from memcache
     * 
     * @param {string} key 
     *  the key used
     * @param {function} callback
     *  the callback containing the value
     */
    get(key, callback) {
      this.client.get(key, (err, value) => {
        if (err) {
          console.error(err);
          callback(err);
        }
        if (value == null) {
          callback(err, null);
        } else {
          callback(err, value.toString());
        }
      });
  }
}
module.exports = MemcachedFactory;

5. To use the class in our code, we have to add the requirement first:

const mf = require('../classes/MemcachedFactory');

6. Here is a small example how the class is used:

mf.getInstance().get(key, (error, value) => {
  if (error) {
    // handle error here
  }else{
    // we have a value
    console.log(`The value is ${value}`); 
  }
});

The getInstance method returns an instance of the class. Then the get method is used with the key to retreive, and a callback method which is called when the request to memcached is completed.

The set method allows to put a key to memcached, and with ttl we can define how long the key is valid and stored.