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Getting started with MongoDB and Mongoose

What is Mongoose?

Mongoose is an “elegant mongodb object modeling for node.js“. If you have used MongoDB before and tried basic database operations, you might have noticed that MongoDB is  “schema less”. When you are looking to implement a more structured database and want to leverage the power of MongoDB, Mongoose is one of the ODM (Object Data Mapping) solutions.

To quickly demonstrate, you run an insert command into a collection named users like


db.users.insert({ name : 'Arvind', gender : 'male'});

And right after that you can run


db.users.insert({ name : 'Arvind', gender : 'male', password : '!@#$'});

and MongoDB will never complain about the variation in the number of columns (key value pairs). This is very flexible. But when you want to keep your data more organized and structured, you would need to maintain that in your server code, writing validation, making sure nothing irrelevant is stored in a collection. And this is where Mongoose makes life easy.

“Mongoose provides a straight-forward, schema-based solution to modeling your application data and includes built-in type casting, validation, query building, business logic hooks and more, out of the box.”

Install Node js & MongoDB

To use Mongoose, we need to have Node js installed, you can find info here.

Start Developing

Let us first create a small playground, where we can have fun. Create a new folder named myMongooseApp. And open terminal/prompt here and run

npm init

This will help us in initializing a new node project. Fill it up as required. Next, we will install Mongoose as a dependency to our project. Run

npm install mongoose --save-dev

then start the MongoDB service by running

mongod

Next, create a new file named index.js at the root of the and then open it up in your favorite editor. And add the below code.

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/myTestDB');

var db = mongoose.connection;

db.on('error', function (err) {
console.log('connection error', err);
});
db.once('open', function () {
console.log('connected.');
});

Here, we require the mongoose package to connect to the DB, and initialize the connection. The name of our Database is myTestDB.

Then run

node index.js

and you should see the connected message. You can also use a node package named nodemon for automatically restarting the node server on changes.
Now, our sandbox is ready to play!

Mongoose Schemas

Schemas are like skeletons. The bare bones of how your data collection will look like. If you are dealing with a collection of users, your schema would look something like this.

Name - String
Age - Number
Gender - String
Date of Birth - Date

And if you are dealing with a collection of products, your schema will look something like this

SKU - String
Name - String
Price - Number
InStock - Boolean
Quantity - Number

You can see the drift. When our data is guarded with a schema like this, the possibility of storing garbage data reduces drastically.

Now we got an understanding of schemas, lets try and build a user schema using Mongoose. Back to index.js and add the below code

var Schema = mongoose.Schema;
var userSchema = new Schema({
name : String,
age : Number,
DOB : Date,
isAlive : Boolean
});

Basic User related fields and their schema types. You can find a list of schema types here.

Next, we will create a model from the schema. Add

var User = mongoose.model('User', userSchema);

Thats it, our User model is ready. We will use this as our base schema to insert users into the database. This way we know that every document in a User collection will have the fields listed on the schema. Lets create a new user instance and save it to DB add

var arvind = new User({
name : 'Arvind',
age : 99,
DOB : '01/01/1915',
isAlive : true
});

arvind.save(function (err, data) {
if (err) console.log(err);
else console.log('Saved : ', data );
});

And you should see something like

Saved : { __v: 0,
name: 'Arvind',
age: 99,
DOB: Fri Jan 01 1915 00:00:00 GMT+0530 (IST),
isAlive: true,
_id: 536a4866dba434390d728216 }

No hassles, no issues. Simple and easy API to interact with Models.

Lets say that we want each model to have a method named isYounger. This method will return true if age is less than 50, false if greater. We can do this by querying the DB for the current user, then checking the conditioning and the returning true or false.

But what if we want to implement this method to all the models of User schema? This is how we do it in Mongoose

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/myTestDB');

var db = mongoose.connection;

db.on('error', function (err) {
console.log('connection error', err);
});
db.once('open', function () {
console.log('connected.');
});

var Schema = mongoose.Schema;
var userSchema = new Schema({
name : String,
age : Number,
DOB : Date,
isAlive : Boolean
});

userSchema.methods.isYounger = function () {
return this.model('User').age < 50 ? true : false;
}

var User = mongoose.model('User', userSchema);

var arvind = new User({
name : 'Arvind',
age : 99,
DOB : '01/01/1915',
isAlive : true
});

arvind.save(function (err, data) {
if (err) console.log(err);
else console.log('Saved ', data );
});

console.log('isYounger : ',arvind.isYounger());

On line 21 we add the method definition. And the result on line 39 will be false. This is a simple handy way of adding methods to your Schema, making it more Object Oriented-ish.

In case you have a password field, you can add a method like encryptPassword(), to encrypt password and comparePassword(), to compare the passwords at login to the userSchema itself. You can read more about password Authentication here.

Out of box Mongoose also provides a few options when the schema is created. For example if you take a look at the below schema declaration, we are passing an option

var userSchema = new Schema({
name : String,
age : Number,
DOB : Date,
isAlive : Boolean
}, {strict : false});

strict:false. Strict option is true by default and it does not allow the ‘non-schema’ key value pairs to be saved. Example:

var arvind = new User({
name : 'Arvind',
age : 99,
DOB : '01/01/1915',
isAlive : true
});

will be saved, where as

var arvind = new User({
name : 'Arvind',
age : 99,
DOB : '01/01/1915',
isAlive : true,
bucketList : [{...}, {...}, {...} ]
});

All of the above will be saved minus the bucketList array, because it was not declared as part of schema. So, no client who consumes your services will be able to dump invalid data into your collections.

Another cool option is collection. If you don’t want your model name to be the same as collection name, you can pass the name as an option like

var userSchema = new Schema({
name : String,
age : Number,
DOB : Date,
isAlive : Boolean
}, {collection : 'appusers'});

You can find a list of other options here.

With Mongoose, You can also add events to your schemas like pre save or post save, where you can perform validations or process data or run other queries in the respective events. These methods are called as Middlewares.

A simple example can be a parallel middleware like

var userSchema = new Schema({
name : String,
age : Number,
DOB : Date,
isAlive : Boolean
})
schema.pre('save', true, function (next, done) {
// calling next kicks off the next middleware in parallel
next();
doAsync(done);
});

You can read more about middlewares here.

 

Thanks for reading. Do comment.
@arvindr21

Read the original blog entry...

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Dharshan is the founder of MongoDirector.com. Previous to MongoDirector Dharshan worked in the Virtualization and Data management groups in Microsoft.

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