Node.JS MongoDB utility library with ORM-like functionality
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Mongoose 1.0

What's Mongoose?

Mongoose is a MongoDB object modeling tool designed to work in an asychronous environment.

Defining a model is as easy as:

var Comments = new Schema({
    title     : String
  , body      : String
  , date      : Date

var BlogPost = new Schema({
    author    : ObjectId
  , title     : String
  , body      : String
  , date      : Date
  , comments  : [Comments]
  , meta      : {
        votes : Number
      , favs  : Number

mongoose.model('BlogPost', BlogPost);

Connecting to MongoDB

First, we need to define a connection. If your app uses only one database, you should use mongose.connect. If you need to create additional connections, use mongoose.createConnection.

Both connect and createConnection take a mongodb:// URI, or the parameters host, database, port.

var mongoose = require('mongoose');


Once connected, the open event is fired on the Connection instance. If you're using mongoose.connect, the Connection is mongoose.connection. Otherwise, mongoose.createConnection return value is a Connection.

Important! Mongoose buffers all the commands until it's connected to the database. This means that you don't have to wait until it connects to MongoDB in order to define models, run queries, etc.

Defining a Model

Models are defined through the Schema interface.

var Schema = mongoose.Schema
  , ObjectId = Schema.ObjectId;

var BlogPost = new Schema({
    author    : ObjectId
  , title     : String
  , body      : String
  , date      : Date

Aside from defining the structure of your documents and the types of data you're storing, a Schema handles the definition of:

  • Validators (async and sync)
  • Defaults
  • Getters
  • Setters
  • Indexes
  • Middleware
  • Methods definition
  • Statics definition
  • Plugins

The following example shows some of these features:

var Comment = new Schema({
    name  :  { type: String, default: 'hahaha' }
  , age   :  { type: Number, min: 18, index: true }
  , bio   :  { type: String, match: /[a-z]/ }
  , date  :  { type: Date, default: }

// a setter
Comment.path('name').set(function (v) {
  return v.capitalize();

// middleware
Comment.pre('save', function (next) {

Take a look at the example in examples/schema.js for an end-to-end example of (almost) all the functionality available.

Accessing a Model

Once we define a model through mongoose.model('ModelName', mySchema), we can access it through the same function

var myModel = mongoose.model('ModelName');

We can then instantiate it, and save it:

var instance = new myModel(); = 'hello'; (err) {


Or we can find documents from the same collection

myModel.find({}, function (err, docs) {
  // docs.forEach

You can also findOne, findById, update, etc. For more details check out the API docs.

Embedded Documents

In the first example snippet, we defined a key in the Schema that looks like:

comments: [Comments]

Where Comments is a Schema we created. This means that creating embedded documents is as simple as:

// retrieve my model
var BlogPost = mongoose.model('BlogPost');

// create a blog post
var post = new BlogPost();

// create a comment
post.comments.push({ title: 'My comment' }); (err) {
  if (!err) console.log('Success!');

The same goes for removing them:

BlogPost.findById(myId, function (err, post) {
  if (!err) {
    post.comments[0].remove(); (err) {
      // do something

Embedded documents enjoy all the same features as your models. Defaults, validators, middleware. Whenever an error occurs, it's bubbled to the save() error callback, so error handling is a snap!

Mongoose interacts with your embedded documents in arrays atomically, out of the box.


Middleware is one of the most exciting features about Mongoose 1.0. Middleware takes away all the pain of nested callbacks.

Middleware are defined at the Schema level and are applied when the methods init (when a document is initialized with data from MongoDB), save (when a document or embedded document is saved).

There's two types of middleware, determined by the signature of the function you define (ie: the parameters your function accepts):

  • Serial Serial middleware are defined like:

    .pre(method, function (next) {

    They're executed one after the other, when each middleware calls next.

  • Parallel Parallel middleware offer more fine-grained flow control, and are defined like

    .pre(method, function (next, done) {

    Parallel middleware can next() immediately, but the final argument will be called when all the parallel middleware have called done().

Error handling

If any middleware calls next or done with an Error instance, the flow is interrupted, and the error is passed to the function passed as an argument.

For example:

schema.pre('save', function (next) {
    // something goes wrong
    next(new Error('something went wrong'));

// later... (err) {
  // err can come from a middleware

API docs

You can find the Dox generated API docs at

Contributing to Mongoose

Cloning the repository

Make a fork of mongoose, then clone it in your computer. The master branch contains the current stable release, and the develop branch the next upcoming major release.

If master is at 1.0, develop will contain the upcoming 1.1 (or 2.0 if the 1 branch is nearing its completion).


  • Please write inline documentation for new methods or class members.
  • Please write tests and make sure your tests pass.
  • Before starting to write code, look for existing tickets or create one for your specifc issue (unless you're addressing something that's clearly broken). That way you avoid working on something that might not be of interest or that has been addressed already in a different branch.