Getting Started
For this tutorial, you will need Express and MongoDB installed on your machine. I covered this in a previous tutorial so refer to it in case you don’t already have them installed.

Mongoose
To install Mongoose, open your terminal screen and enter the following:

$ npm install mongoose

To automatically build out an application template for your application, navigate to the directory where you wish to create your application and run the following code:

mkdir MongooseExample
cd MongooseExample
express -c stylus
npm install -d

What this does:

• create the directory for your application.
• create your application template using the jade template engine and the stylus css engine.

You should now be able to run your application and see a generic Express application.

node app.js

Navigate to http://localhost:3000

Installing Dependencies
First we need to add our dependency for Mongoose. Open your package.json and add the following code:

{
  "name": "application-name",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "start": "node app"
  },
  "dependencies": {
    "express": "3.1.0",
    "jade": "*",
    "stylus": "*",
    "mongoose" : "3.2.0"
  }
}

Everything should have already been there with the exception of "mongoose" : "3.2.0". Once you have saved the file run the following code to download and install the nodejs client for mongoose:

npm install -d

The Code
db.js
Now we’re going to create a file called db.js to configure MongoDB and our schema.

var mongoose = require( ‘mongoose‘ );
var Schema   = mongoose.Schema;

var Comment = new Schema({
    username : String,
    content  : String,
    created  : Date
});

mongoose.model( ‘Comment‘, Comment );

mongoose.connect( ‘mongodb://localhost/express-comment‘ );

Save this file in the same directory as app.js. The first thing we do is include mongoose and get a reference to schema. Everything in mongoose is derived from a schema. Next, we create our Comment schema and compile it into a model. Last we open a connection to our express-comment database on our locally running instance of MongoDB.

app.js
Open app.js and add require( ‘./db‘ ); at the top of the file. It should look this:

/**
 * Module dependencies.
 */

require( ‘./db‘ ); //for mongoose. Require this first!!!

var express = require(‘express‘)
  , routes = require(‘./routes‘)
  , user = require(‘./routes/user‘)
  , http = require(‘http‘)
  , path = require(‘path‘);

var app = express();

app.configure(function(){
  app.set(‘port‘, process.env.PORT || 3000);
  app.set(‘views‘, __dirname + ‘/views‘);
  app.set(‘view engine‘, ‘jade‘);
  app.use(express.favicon());
  app.use(express.logger(‘dev‘));
  app.use(express.bodyParser());
  app.use(express.methodOverride());
  app.use(app.router);
  app.use(require(‘stylus‘).middleware(__dirname + ‘/public‘));
  app.use(express.static(path.join(__dirname, ‘public‘)));
});

app.configure(‘development‘, function(){
  app.use(express.errorHandler());
});

app.get(‘/‘, routes.index);
app.get(‘/users‘, user.list);

http.createServer(app).listen(app.get(‘port‘), function(){
  console.log("Express server listening on port " + app.get(‘port‘));
});

index.js
Open index.js and add the following code:

var mongoose = require( ‘mongoose‘ );
var Comment = mongoose.model( ‘Comment‘ );

exports.index = function ( req, res ){
  Comment.find( function ( err, comments, count ){
    res.render( ‘index‘, {
        title : ‘Comment System with Mongoose and Node‘,
        comments : comments
    });
  });
}; 

exports.create = function ( req, res ){
  new Comment({
    username : req.body.username,
    content : req.body.comment,
    created : Date.now()
  }).save( function( err, comment, count ){
    res.redirect( ‘/‘ );
  });
};

The first thing we do is require mongoose and the Comment model before we can use it. The index function is replaced with one that queries the database for comments and returns them to the index page. Comment.find is used to pull all comment collections. The create function saves a new comment from form values. We’ll create the form in a minute. First, add the following line to app.js: app.post( ‘/create‘, routes.create );
It should now look like this:

app.get(‘/‘, routes.index);
app.post( ‘/create‘, routes.create );

index.jade
Open index.jade and add the form and a loop to show the comments under the form.

extends layout

block content
  h1= title
  div.addCommentForm
        form( method="post", action="/create")
            div
                div
                    span.label Name :
                    input(type="text", class="nameTxt", name="username")
                div
                    span.label Comment :
                    textarea(name="comment")
                div#addCommentSubmit
                    input(type="submit", value="Save")
  br
  br
  #comments
    - each comment in comments
      div.comment
        div.name= comment.username
        div.created_at= comment.created
        br
        div.content= comment.content 
        hr
  

style.styl
You will need to pretty up the page so open style.styl and add the following code:

body
  padding: 50px
  font: 14px "Lucida Grande", Helvetica, Arial, sans-serif
a
  color: #00B7FF
.addCommentForm
    width 450px
  input[type =text]
    width 200px
    margin-left 38px
  textarea
    width 200px
    margin-left 10px
  input[type =button], input[type =submit]
    clear both
    margin-left 85px
    display block
  .label
      text-align right !important
      display block
      float left
#comments
  .name
    float left
  .created_at
    float right
  .content
    clear both

Now re-run the application and you should be able to add comments which will display under the form. Navigate to localhost:3000 and make sure you have MongoDB up and running.

node app.js

Download the source code at https://github.com/ijason/NodeJS-Mongoose

Getting Started with Mongoose and Node.js – A Sample Comments System | Dev Notes