Creating an MVC Express.js Application (Part 4): Relational Data in MongoDB

In this section we will look at another interesting aspect of creating a web application using Node.js, Express, and MongoDB: referencing other data in the database. MongoDB is part of the NoSQL class of databases (as opposed to the traditional relational databases that have been so prevalent for so long). NoSQL databases store records as documents as opposed to relational databases which store records as rows in tables. Documents in NoSQL databases are basically collections of key value pairs sort of like JSON objects. As the MongoDB documentation describes in the introduction…

A record in MongoDB is a document, which is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents.

You can find many articles out on the web discussing the difference between NoSQL databases and relational databases. MongoDB is a solution to a common problem and like with many things it has its advantages and its drawbacks.

But even with their structure, NoSQL database documents still have need to store references to other objects within them (somewhat like foreign keys). We have been creating data models of books in previous examples in this tutorial that have a “title” field, an “author” field, and an “isPublished” field. We have been storing the author as a string value. But really in a real-world application we’d more likely want to store a reference to an author that exists in an authors collection elsewhere. That way we could store additional information about an author or show a collection of books written by the same author. When you start relating and connecting data in this manner your application becomes truly dynamic and useful

Setup

So let’s create an “AuthorModel” and all of the scaffolding to put an “authors” section in the database. Like we’ve done before, we’ll want to follow the same process: define our model schema for our “AuthorModel,” add routes, add controllers, and add views. We will move fairly quickly through this. A lot of what we are doing was covered earlier in this tutorial. If there are any parts that seem unclear, please go back and review the content presented earlier to get a refresher on how this application is being structured.

So let’s start by defining our author schema in our Models.js file. This one will be a bit simpler than our book model schema. All we need to add here is a name. What will be important later on is the author _id value that we can associate with a book as a reference field…

var Author = new mongoose.Schema({
    name: String
});
var BookModel = mongoose.model('Book', Book);
var UserModel = mongoose.model('User', User);
var AuthorModel = mongoose.model('Author', Author);
module.exports = {
    BookModel: BookModel,
    AuthorModel: AuthorModel,
    UserModel: UserModel
};

And let’s continue with adding our author routes to the router.js file making sure to add a refenrece to our soon-to-be-created AuthorsController…

var HomeController = require('./controllers/HomeController');
var BookController = require('./controllers/BookController');
var AuthorController = require('./controllers/AuthorController');
// Routes
module.exports = function(app){
    // Main Routes
    app.get('/', HomeController.Index);
    app.get('/other', HomeController.Other);   
    // Book Routes
    app.get('/books', BookController.Index);
    app.get('/books/add', BookController.BookAdd); 
    app.post('/books/add', BookController.BookCreate); 
    app.get('/books/edit/:id', BookController.BookEdit);
    app.post('/books/edit', BookController.BookUpdate); 
    app.get('/books/delete/:id', BookController.BookDelete);     
    // Author Routes
    app.get('/authors', AuthorController.Index);
    app.get('/authors/add', AuthorController.AuthorAdd); 
    app.post('/authors/add', AuthorController.AuthorCreate); 
    app.get('/authors/edit/:id', AuthorController.AuthorEdit);
    app.post('/authors/edit', AuthorController.AuthorUpdate); 
    app.get('/authors/delete/:id', AuthorController.AuthorDelete);  
}; 

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Creating an MVC Express.js Application (Part 3): Data Access & Validation With MongoDB

In previous installments we looked at getting started with creating an Express.js MVC application, creating controllers and views. And then we looked at middleware and creating a config file to store application constants.

Now we will look at something that truly makes an Express.js application dynamic (and fun): data-access… which essentially boils down to the use of a database to store, retrieve, and manipulate information.

Like many things in technology, people will always argue about what is the “best” way to do something and what the best technologies to use for doing that something are. And the way in which an application should store data is not going to be excluded from this discussion (read: Internet flame-war). It is not really part of our purposes to argue what is “best” or “better” when it comes to data-access, but it is probably worth pointing out that a lot of the Express.js and Node.js communities seem to have embraced NoSQL databases such as MongoDB, and CouchDB. There is even a full “stack” you will hear mentioned known as the MEAN stack (MongoDB, Express, AngularJS, and Node.js) — just like you’d hear of a LAMP stack (Linux, Apache, MySQL, and PHP). The inclusion of MongoDB in this shows its prominence in developer preference in Express and Node applications.

So, it is probably worth knowing a bit about how to use a MongoDB database in a Node.js and Express.js application because you are more than likely to come across it at some point in your life as a developer. So, resultantly, we’ll utilize MongoDB in our application.

Installing MongoDB

Head on over to MongoDBs home page and download MongoDB for your OS. You’ll probably just want to pick the standard install and won’t need any fancy cloud services at this point. Be sure to read through the installation section in the docs section of the site. and do the subsequent tutorials to make sure you can test out that MongoDB was installed correctly. There is a “Getting Started” section that should walk you through this where you can try out creating, reading, inserting and deleting data a sample MongoDB database.

After you have installed MongoDB create a new folder in the root of your application can call it “db”. This is where we are going to store our database and we’re going to point MongoDB to put all the files for this database in here.

To start things up, next go to the directory where you installed Mongo and navigate into the bin directory and open a command window. So on Windows, for example, if you installed in the C:\mongodb directory, you would open a command window or shell in C:\mongodb\bin. You could also get there by opening a command window anywhere and typing

cd "C:\mongodb\bin"

Then you would type the following into the command window where we should specify the path to the “db” folder we just created. So wherever your application lives on your system you’ll want to specify that path by running the following command.

mongod --dbpath "C:\path\to\application\db"

or if you’re using BASH, something like this…

mongod --dbpath /c/path/to/application/db

If all goes well, you should see a message saying that MongoDB is waiting for connections. By default at the time of this writing, the version of MongoDB being used waits for connections on port 28017… so you should see that reflected somewhere in the messaging. Leave this running by leaving this window open (you can minimize if you like).

NOTE: When you first run this command, MongoDB will create all the files it needs in the “db” folder we created, so you should see a number of files pop up in there. Some are quite large.

Now that we have MongoDB installed and we can connect to it, lets write some Node.js code to do some data operations! Woo hoo! Like with so many things we have done before, we will utilise a module to act as a wrapper for our data access with MongoDB. Remember, you could always set things up and write your own code in Node.js for accessing data. Using modules is basically just a way to circumvent all of that grunt work and manual labor involved in those processes. If somebody else has already done the heavy lifting in making a module, might as well make use of it.

Installing Mongoose

I am going to use a popular module for accessing MongoDB on npm called Mongoose.js (which like pretty much all Node.js modules is avialble on npm). There are probably some other modules that you could use, we’re just going to go with this one to start. So as we have done before when we are adding a new module, we need to update our package.json with a new reference to Mongoose. We will also add another module called body-parser which is going to be useful for getting data out of forms so we can save it in our database.

{
    "name": "MVC-Express-Application",
    "description": "An Express.js application using the MVC design pattern...",
    "version": "0.0.1",
    "dependencies": {
        "express": "4.4.4",
        "body-parser": "1.4.3",	
        "express-handlebars": "1.1.0",
        "morgan": "1.1.1",
        "errorhandler": "1.1.1",
        "mongoose": "3.8.8"
    }
}

Then again, we should open a shell in our project root directory and run

$ npm install

which will pull down all the Mongoose and body-parser files.

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