Michael Lefkowitz

Building a URL Shortener with MongoDB, Express, and Node.js

May 05, 2016

Personally, it wasn’t until I had done a few laps around Node.js until I finally felt like I had got my head around what it was capable of. So when I started the URL Shortener Microservice project, I should have expected a similar struggle for my first MongoDB application. But I didn’t.

When I had first tested the waters of learnyoumongo, I immediately felt I was in over my head. I had very little prior experience working with databases, so I took a step back and began to research the fundamentals a bit further. After I felt comfortable with databases, I took a few SQL courses to familiarize myself with relational databases. Next, I dived back into MongoDB with some great tutorials via Treehouse and Code School. At this point, I felt comfortable with the basics of querying and inserting with MongoDB, but the next step of incorporating the M into the MEAN stack was my next challenge. After a failed attempt to translate coligo’s tutorial into an API, I started from scratch.

That was the best decision I had made yet. Tackling this project step-by-step reminded me that this was the best way to learn, one small step at a time. And now that I’ve finished this project, I’m going to walk through the build process one more time. I hope this tutorial is helpful, and if anyone has any questions, comments, or critiques, please feel free to share them.

First, go ahead and initialize a new git repo (I’m going to call mine url-shortener-microservice), jump into it, and setup a directory to test out our database - git init url-shortener-microservice cd url-shortener-microservice

Next, setup your project’s npm and fill in any information you find necessary. I’m just going to roll through and leave all the options as their default. npm init

Now, let’s use express-generator to scaffold our app quickly. If you get a warning about the destination not being empty, just type y to continue. If you haven’t used express-generator before, you’ll need to first install it globally. express npm install

Also, let’s create a .gitignore file to stop tracking the node_modules folder echo node_modules > .gitignore

And for the final piece of the setup, let’s install all of the additional npm packages we’re going to need for this project npm install mongodb --save npm install shortid --save npm install valid-url --save

Go ahead and run your app and connect to localhost:3000 in your browser. You should be seeing “Welcome to Express”. If you don’t have nodemon installed, you’ll want to install that globally too. nodemon app


Now, startup your MongoDB daemon mongod

Let’s setup our database and collection. Open a third tab on Terminal and run mongo. Then, we’ll create a database called url-shortener-microservice. mongo use url-shortener-microservice

Okay this time, we’re actually done with the setup.

Open up your routes/index.js file. I’m not going to touch on building out your / route, that’ll be up to you. So, let’s do some importing of modules. First and foremost, you’re going to need to import MongoDB. Then, import the shortid module. This will help us generate unique links for each url we pass through. And finally, import the valid-url module. As the name implies, we’re going to use that to verify that our urls are formatted properly.

var mongodb = require("mongodb");
var shortid = require("shortid");
var validUrl = require("valid-url");

Alright let’s finally get to the code here. First, we’re going to work on the creation of new links. Create a new GET route that looks like this:

router.get("/new/:url(*)", function(req, res, next) {});

The (*) piece in our :url(*) parameter will allow us to pass in properly formatted links. Without it, Express will get confused with the forward slashes in URLs and think they’re additional parts of the route. You can also use regular expressions to accomplish this.

Let’s pause here and make sure everything is still working properly. Drop a console.log into your new route that utilizes the request parameter and test it out. My code looks like this so far:

router.get("/new/:url(*)", function(req, res, next) {

And when I try to access http://localhost:3000/new/http://www.lefkowitz.me in my browser, I see http://www.lefkowitz.me in the browser.

Alright. So far so good.

Now, let’s get our connection to our local MongoDB database up and running. We’ll create a variable underneath where we imported our MongoDB module at the top in order to store our connection information. I’m going to call my variable mLab, as the database will eventually need to move to the cloud and I’m going to use mLab’s free offering to host it. Also, create a variable called MongoClient to host MongoDB’s connect command. var mLab = "mongodb://localhost:27017/url-shortener-microservice"; var MongoClient = mongodb.MongoClient

Then, back in our recently created route, replace the console.log we created with the following:

MongoClient.connect(mLab, function(err, db) {
  if (err) {
    console.log("Unable to connect to server", err);
  } else {
    console.log("Connected to server");

Now, whenever this route is accessed, MongoDB will connect to our local database and print a message to the console.

Alright, jump below the successful connection console.log in your else statement and create two more variables. The first will set up our collection and make it a bit easier to access, and the second will be set to our url parameter.

var collection = db.collection("links");
var params = req.params.url;

Now, we’re going to create the function that imports a link to the database and returns a short link. We’ll call it newLink and it will accept a callback that will close the database connection once it’s run.

var newLink = function(db, callback) {};

newLink(db, function() {

Okay it’s been a while since we’ve run any tests, so let’s see if we’re on track so far by importing some documents into our links collection. Inside of our newLink function, insert the following:

var insertLink = { url: params, short: "test" };

This will create a new object with our passed-thru parameters set to the url key, and “test” set to the short key. Then, it will push that object into a document in our database. And finally, we’re going to send our URL parameter to output again, just like in our last test.

Now, fire up your browser and point it to http://localhost:3000/new/http://www.lefkowitz.me

Once you see http://www.lefkowitz.me output onto the page, open up your mongo tab in Terminal and type db.links.find(). You should see something like this:

  "_id": ObjectId("572a780bcf012a51ee123b3b"),
  "url": "http://www.lefkowitz.me",
  "short": "test"
Fetched 1 record(s) in 7ms

Tip - To make working in MongoDB a bit easier in Terminal, do a global install of mongo-hacker

Alright let’s keep moving. We’re going to want to do three things when a URL is passed thru as a parameter:

  1. Check if the URL is valid
  2. If it is, assign a random set of characters to it
  3. Pass the URL and the random characters into our collection

So first, create an if/else statement utilizing our valid-url module in the newLink function. Replace the three lines we dropped in there during our last test.

if (validUrl.isUri(params)) {
  // if URL is valid, do this
} else {
  // if URL is invalid, do this

If a URL is valid, generate a short code. Then, create a new object. Insert that object into the collection as a new document like we did in our test. And finally, let’s push some JSON to our browser.

var shortCode = shortid.generate();
var newUrl = { url: params, short: shortCode };
res.json({ original_url: params, short_url: "localhost:3000/" + shortCode });

If the URL isn’t valid, make sure to output an error. res.json({ error: "Wrong url format, make sure you have a valid protocol and real site." });

Currently, this is what our index.js file should look like. Hopefully yours looks the same and you’re successfully pushing new links into your database. We’re halfway through the meat of this project!

Now, let’s look into redirection. We’re going to set up another route that once again connects to our database, runs a function, and closes the database once that function has run. The bulk of it will look similar to our last route:

router.get("/:short", function(req, res, next) {
  MongoClient.connect(mLab, function(err, db) {
    if (err) {
      console.log("Unable to connect to server", err);
    } else {
      console.log("Connected to server");

      var collection = db.collection("links");
      var params = req.params.short;

      var findLink = function(db, callback) {};

      findLink(db, function() {

Now that we have that setup, we’re going to want to take the parameter that has been passed through and find it in our collection. I’m going to use the .findOne query since the short codes are unique values, we don’t want to waste resources looking for additional matches. We’re also going to limit the query to only return the url field, as all other fields are unnecessary for our needs. Our query is going to look like this: collection.findOne({ "short": params }, { url: 1, _id: 0 })

After the query is run, we’re going to pass in a function. If a document is found, the function will return it. Once it’s returned, we’re going to use a res.redirect() to redirect the browser to the value of the returned key/value pair. If the document is not found, we’ll output another JSON error.

collection.findOne({ short: params }, { url: 1, _id: 0 }, function(err, doc) {
  if (doc != null) {
  } else {
    res.json({ error: "No corresponding shortlink found in the database." });

And that’s it. We now have a functioning URL shortener! Now let’s make some tweaks to improve it. In our first route, let’s built an if/else statement that queries our database before we drop a link into it to check if that link already exists, so that we can keep the size of our database down. It will look similar to the query we just built, except this time we’re looking for the url and we’re only returning the short code. This will run at the top of the newLink function, and will be followed by an else statement that runs the original code to create a new link if the query is unsuccessful.

collection.findOne({ "url": url }, { short: 1, _id: 0 }, function (err, doc) {
  if (doc != null) {
res.json({ original_url: url, short_url: local + '/' + doc.short });

At this point, our index.js file should look like this. We’ve got a few more minor tweaks to do, and then we can move our database to mLab. First, I think having underscores and dashes as options in our short codes is a bit confusing. Underneath where we imported our shortid module, let’s set a new list of characters that replaces _ and - with $ and @. shortid.characters('0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$@');

Next, let’s make our JSON output a bit more dynamic so we don’t have to update the string when we push it to deployment. In the /new/:url(*) route, add var local = req.get('host'); + "/" above the newLink function. Then, replace the localhost:3000/ string in both JSON responses to your new local variable.

Alright, let’s move our database onto a remote server. I’m using mLab, but if you’re more comfortable with an alternative, go right ahead and use that. In mLab, hit the “Create new” button, choose “Single-node”, and then select “Sandbox”. For consistency, let’s use “url-short” as our database name. Once you’ve created your database, it’s going to ask you to create a user in order to access your database. For this example, I’ll use “user” and “pass” - but you’re probably going to want to use something a bit more secure in your app. Alright, now grab the link that’s presented and replace your mLab variable with it. Make sure to drop in your username and password in the corresponding placeholder fields. var mLab = "mongodb://user:pass@ds015962.mlab.com:15962/url-shortener-microservice";

Now, back to the browser to see if it’s working. I’m going to attempt to access http://localhost:3000/new/http://www.lefkowitz.me again. I’m seeing a JSON response, so that’s a good sign. Now let’s hit the “Collections” tab in mLab, refresh the page, and see if our collection is there.

Yup, we have a links collection with one document in it. Success! mlab

Before we push this to Heroku, you’re going to want to exclude your database username/password information from your Github repo. Create a file called config.js in your root directory, and paste the following into it:

var config = {};

config.db = {};

config.db.host = 'user:pass@ds015962.mlab.com:15962;
config.db.name = 'url-shortener-microservice';

module.exports = config;

Then, in your index.js file. Drop the following in between your mongodb and MongoClient variables:

var config = require("../config");
var mLab = "mongodb://" + config.db.host + "/" + config.db.name;

Now, in your .gitignore file, add config.js. Push your code to Github, and then create a new branch called heroku and remove config.js from your .gitignore file. Push your app to Heroku, grab a beer, and pat yourself on the back.

Here’s the final code.

That’s it. My personal next steps for this project are to DRY it out a bit, create an option for custom short codes, and then dive into a dashboard with some analytics. Again, if you have any questions, comments, or critiques, please feel free to share them.