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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Creating an MVC Express.js Application (Part 2): Middleware and Configuration

Previously, in an earlier installment we discussed some initial considerations for creating an application in Express.js following the Model View Controller (MVC) design pattern. We’ll pick up where we left off in what follows. The focal point will center around middleware and configuration…

Middleware

One of the things that we are going to want to implement in our application is middleware. There is a pretty good list of Express.js middleware in the Express.js project. Middleware is an important component of Express.js applications. You couple probably think of a middleware function or method as a function that runs on every request/response cycle at whatever point you want to specify. For example, if you wanted to see if the current user who is making the request is authenticated on every single request, you might have this authentication check run in a middleware function before issuing the response. That’s just one example, but there are many other pieces of functionality that you can run within middleware functions.

So let’s add some of the common Express.js middlewares. One useful middleware utility that we can use is a logging component. This will give us information about all of the requests made as our application runs. Express.js uses something called Morgan to accomplish this.

To add middleware, we’re going to want to add it to our package.json file as a dependency. So let’s update our package.json file to look like the following

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

Don’t forget that we have to install our new module as well. Fortunately, Node.js and npm make this easy. All we have to do is run $ npm install again and all of our packages will be updated…

$ npm install

Now that our dependency is installed, we need to add a reference to it in our main application file…

var logger = require('morgan');

Let’s add the following lines of code to our main app.js file…

/* Morgan - https://github.com/expressjs/morgan
 HTTP request logger middleware for node.js */
app.use(logger({ format: 'dev', immediate: true }));

Now if we run our application and look at our CLI window we can see all the requests being output on every request response cycle. And just like that, we have made use of our first middleware.

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Creating an MVC Express.js Application

Express.js is probably currently the most popular Node.js framework for building web applications and APIs. It has a good history, a good community around it, lots of modules built for it, and a fairly solid reputation.

In what follows we’re going to walk through how to build an Express.js application using the Model View Controller (MVC) design pattern. It’s likely that we’ll do this tutorial in multiple parts.We’ll start out with a simple application structure and then we’ll move on by adding more complex concepts like authentication, dynamic routing, and reading from and writing to a database.

To start, it’s a good idea to have some background on both Node.js and Express so you know some of the terminology and philosophy behind what is being discussed. If you are not entirely familiar with Express.js there is an introduction to it here. And if you’re not entirely familiar with Node.js there is a primer on Node.js here.

At the time of this writing Express is at version 4.X. If you are reading this at a later point, it’s possible that the latest version differs quite significantly from this. Be sure to check out the Express.js homepage to find information on how to properly set things up using the most current version of Express. However, it may be the case that the steps followed in this tutorial will not be fully compatible with the most recent version of Express.js

package.json

To start we’re going to want to create a package.json file. You can read more about pakcage.json here. package.json will define some metadata type things like the name and version of the application, but most importantly, it will specify what modules you will need to download and run the application. You can read more about modules in Node.js here as well as in any good introduction to Node.js. Express is itself a Node.js module and it makes use of other Node.js modules. Some modules like “http” are core Node.js modules (part of the Node.js core) and some like express.js are third-party. Core Node.js modules will always be available to your application because it is running on Node.js

So our sample package.json file will look like the following…

{
    "name": "MVC-Express-Application",
    "description": "An Express.js application using the MVC design pattern...",
    "version": "0.0.1",
    "dependencies": {
        "express": "4.4.4",		
    }
}

One item of note: the name of any given package cannot have any spaces. This is to ensure that installation of packages is easy and consistent across all environments.If people were ever wanting to install our application as a module on npm (if we ever put our application on npm) by running $ npm install MVC-Express-Application it would not work if the package was named MVC Express Application. If we ran $ npm install MVC Express Application, the CLI would get confused.

Now if we run the following from the directory where our package.json file resides

$ npm install

all of the dependencies that we have specified will be downloaded and installed into a “node_modules” directory. The great thing about this is that if we need to update the versions of our modules or add new ones, we can just add or edit this package.json file and run “npm install” again. The npm installer will figure out all of the files needed. We are limited to the modules we are installing right now, but we will be adding a lot more to this later.

Application

Next we’ll want to create an “app.js” file. This file is the kickoff/entry point of our application when it starts up. This is akin to the main() function you’d find in C++ or Java.

The first components we’re going to want to add are here…

var express = require('express');

This loads up the express module. We can now refer to it in our code.

A lot of the modules we’ll be loading up are part of the Express.js project itself. There are many useful items that our application will be utilizing at various times throughout our application. As is described in the Node.js documentation on modules, Node.js modules can be loaded via references to filenames so long as those filenames are not named the same as reserved core Node.js modules, e.g. the “http” module.

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Backbone.js Models

Models in Backbone.js are the “data houses” for Backbone applications. They hold the data that gets fetched from the server and they get passed to the Backbone Views so that the views can display them. When users create or update data (by filling out a form and clicking a button or by some other means), that data will be housed within a model and then sent up to the server for processing.

To define a Backbone model, you have to simply have to extend the Backbone Model.

var Artist = Backbone.Model.extend({});

And then to use it we could create a new insatance…

var artist = new Artist();

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