The MEAN Stack: MongoDB, ExpressJS, AngularJS and Node.js



January 2017 An updated post is available: Introducing the MEAN and MERN stacks.

By Valeri Karpov, Kernel Tools engineer at MongoDB and and co-founder of the Ascot Project

A few weeks ago, a friend of mine asked me for help with PostgreSQL. As someone who’s been blissfully SQL-­free for a year, I was quite curious to find out why he wasn’t just using MongoDB instead. It turns out that he thinks MongoDB is too difficult to use for a quick weekend hack, and this couldn’t be farther from the truth. I just finished my second 24 hour hackathon using Mongo and NodeJS (the FinTech Hackathon co­sponsored by 10gen) and can confidently say that there is no reason to use anything else for your next hackathon or REST API hack.

First of all, there are huge advantages to using a uniform language throughout your stack. My team uses a set of tools that we affectionately call the MEAN stack:­ MongoDB, ExpressJS, AngularJS, and Node.js. By coding with Javascript throughout, we are able to realize performance gains in both the software itself and in the productivity of our developers. With MongoDB, we can store our documents in a JSON-­like format, write JSON queries on our ExpressJS and NodeJS based server, and seamlessly pass JSON documents to our AngularJS frontend. Debugging and database administration become a lot easier when the objects stored in your database are essentially identical to the objects your client Javascript sees. Even better, somebody working on the client side can easily understand the server side code and database queries; using the same syntax and objects the whole way through frees you from having to consider multiple sets of language best practices and reduces the barrier to entry for understanding your codebase. This is especially important in a hackathon setting: the team may not have much experience working together, and with such little time to integrate all the pieces of your project, anything that makes the development process easier is gold.

Another big reason to go with MongoDB is that you can use it in the same way you would a MySQL database (at least at a high level). My team likes to describe MongoDB as a “gateway drug” for NoSQL databases 
because it is so easy to make the transition from SQL to MongoDB. I wish someone had told me this when I first starting looking into NoSQL databases, because it would have saved me a lot of headaches. Like many people, I was under the impression that CouchDB would be easier to use, while the performance improvements from MongoDB were something I could take advantage only once I had gotten my feet wet with CouchDB. Instead CouchDB ended up being much more difficult to work with than I anticipated, largely because it uses custom Map­Reduce functions to query data, rather than the more traditional SQL queries I
 was used to. When I finally switched I was surprised to find that with MongoDB I could still write queries and build indices; the only difference is that the queries are written in JSON and query a flexible NoSQL database.

As a NoSQL database, MongoDB also allows us to define our schema entirely on the code side. With an RDBMS you’re faced with the inescapable fact that the objects in your database are stored in a format that is unusable by your front­end and vice versa. This wastes precious time and mental energy when you inevitably run into a data issue or need to do some database administration. For example, if you change your ActiveRecord schema in Ruby on Rails, you have to run the “rake” command to make sure your SQL columns stay in sync with your schemas. This is a clear violation of the age­-old programming principle D.R.Y.­ (Don’t Repeat Yourself). In contrast, MongoDB doesn’t care what format the documents in your collections take (for the most part anyway). This means that you spend a lot less time worrying about schema migrations, because adding or removing data items from your schema doesn’t really require you to do anything on the database side.

At this point I should note that to get the most out of MongoDB in your MEAN stack, you’re going to want to take advantage of MongooseJS. Mongoose is a schema and general usability tool for Node that lets you use MongoDB while being as lazy as you want. For example, with Mongoose we can define a schema in JSON:

 var UserSchema = new Mongoose.Schema({
username : { type : String, validate: /\S+/, index : { unique : true } }, profile : {
name : {
first : { type : String, default : “” } last : { type : String, default : “” }
} }

We can then create a model by mapping our schema to our MongoDB collection:

 var User = db.model('users', UserSchema);

For all of the Ruby on Rails + ActiveRecord fans out there, note that this User object we’ve created above now allows us easy access to the basic features you would normally associate with ActiveRecord. For example, we can do thing like:

User.findOne({ username : 'vkarpov' }, function(error, user) { /* user is either undefined or a user with username vkarpov */ });

User.findOne({ _id : }, function(error, user) { /* user with ID defined by the hex string in */ });
User.find({ '' : 'Valeri' }, function(error, users) { /* users is a list with users with first name Valeri */ });
var user = new User({ username : 'vkarpov' });, user) { /* Saves user with default values for and .last into 'users' collection */ });
var user2 = new User({ username : 'v karpov' });, user) { /* Error – regular expression validation for username failed */ });

Another powerful tool that MongoDB and MongooseJS provide is the ability to nest schemas. You’ll notice that in the User schema above we have “profile” and “name” objects that are part of a nested schema. This is a simple and useful design choice that illustrates how powerful nested schemas can be. Suppose that we want to give our user the ability to edit their first and last name, but not their username. Assuming the website has a /profile route where our user can the change first and last names, the Javascript front­end will get a JSON object as the result of a call to User.findOne on the backend. After the user modifies their profile, the front­end makes a POST request to /profile.json with the user object in JSON as the body. Now on the backend (using ExpressJS syntax) we can simply use:

function(req, res) {
user.profile = req.body.profile;, user) { res.redirect('/profile'); }); } }

That’s it. Mongoose takes care of validating of the profile information, so we don’t have to change the POST /user.json route if we change the User schema, and there is no way the username field can be modified. We could do the same thing when using Ruby on Rails and ActiveRecord, but this would require having a separate Profile schema in a separate table, meaning that among other things we’d incur a performance penalty because of the extra underlying join operation.

MongoDB is the bedrock of our MEAN stack, and you should strongly consider using it for your next project. You can write your entire stack in one language, have schemas for ease of use on top of a flexible and performant NoSQL database, and nest schemas when you don’t truly need to have separate collections. All
of this adds up to you spending more of your precious hackathon hours building the other cool aspects of your product and less time figuring out how your objects translate between different levels of the stack.

By the way, MongoDB and MEAN are useful well beyond hackathons­ we use this approach for all of our commercial products, most recently The Ascot Project. Want to read more about the MEAN stack or how we use MongoDB? Check out my development blog.

Check out the Ascot Project at the next MongoDB User Group in New York City

More Information

This post was updated in January 2015 to include additional resources and updated links.

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