MongoDB is widely used with Node.js applications, a sign of which is the popular MEAN acronym: MongoDB (or MySQL), Express, Angular, and Node.js. MongoDB is one of the leading NoSQL databases. It is described as a scalable, high-performance, open source, document-oriented database. It uses JSON-style documents with no predefined, rigid schema and a large number of advanced features. You can visit their website for more information and documentation at http://www.mongodb.org.

Mongoose is a popular ORM for MongoDB (http://mongoosejs.com/). In this section, we'll use the native MongoDB driver instead, but Mongoose is a worthy alternative.

You will need a running MongoDB instance. The compose.io (https://www.compose.io/) and ScaleGrid.io (https://scalegrid.io/) hosted service providers offer hosted MongoDB services. Nowadays, it is straightforward to host MongoDB as a Docker container as part of a system built of other Docker containers. We'll do this in Chapter 11, Unit Testing and Functional Testing.

It's possible to set up a temporary MongoDB instance for testing on, say, your laptop. It is available in all the operating system package management systems, and the MongoDB website has instructions (https://docs.mongodb.org/manual/installation/).

Once installed, it's not necessary to set up MongoDB as a background service. Instead, you can run a couple of simple commands to get a MongoDB instance running in the foreground of a command window, which you can kill and restart any time you like.

In one command window, run the following:

$ mkdir data
$ mongod --dbpath data

In another command window, you can test it as follows:

$ mongo
MongoDB shell version: 3.0.8
connecting to: test
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
  http://docs.mongodb.org/
Questions? Try the support group
  http://groups.google.com/group/mongodb-user
> db.foo.save({ a: 1});
WriteResult({ "nInserted" : 1 })
> db.foo.find();
{ "_id" : ObjectId("56c0c98673f65b7988a96a77"), "a" : 1 }
> 
bye

This saves a document in the collection named foo. The second command finds all documents in foo, printing them out for you. The _id field is added by MongoDB and serves as a document identifier. This is useful for testing and debugging. For a real deployment, your MongoDB server must be properly installed on a server. See the MongoDB documentation for these instructions.