What's Mongoose?

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

Defining a model is as easy as:

var Comment = new Schema({
    title     : String
  , body      : String
  , date      : Date
});

var BlogPost = new Schema({
    author    : ObjectId
  , title     : String
  , body      : String
  , buf       : Buffer
  , date      : Date
  , comments  : [Comment]
  , meta      : {
      votes : Number
    , favs  : Number
  }
});

var Post = mongoose.model('BlogPost', BlogPost);

Installation

The recommended way is through the excellent NPM:

$ npm install mongoose

Otherwise, you can check it in your repository and then expose it:

$ git clone git://github.com/LearnBoost/mongoose.git node_modules/mongoose/

And install dependency modules written on package.json.

Then you can require it:

require('mongoose')

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, options.

var mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/my_database');

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
• DBRefs

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: Date.now }
  , buff  :  Buffer
});

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

// middleware
Comment.pre('save', function (next) {
  notify(this.get('email'));
  next();
});

Take a look at the example in examples/schema.js for an end-to-end example of a typical setup.

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');

Or just do it all at once

var MyModel = mongoose.model('ModelName', mySchema);

We can then instantiate it, and save it:

var instance = new MyModel();
instance.my.key = 'hello';
instance.save(function (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 this link.

Important! If you opened a separate connection using mongoose.createConnection() but attempt to access the model through mongoose.model('ModelName') it will not work as expected since it is not hooked up to an active db connection. In this case access your model through the connection you created:

var conn = mongoose.createConnection('your connection string');
var MyModel = conn.model('ModelName', schema);
var m = new MyModel;
m.save() // works

vs

var conn = mongoose.createConnection('your connection string');
var MyModel = mongoose.model('ModelName', schema);
var m = new MyModel;
m.save() // does not work b/c the default connection object was never connected

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' });

post.save(function (err) {
  if (!err) console.log('Success!');
});

The same goes for removing them:

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

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

Middleware are defined at the Schema level and are applied for 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:

• Serial Serial middleware are defined like:

    .pre(method, function (next, methodArg1, methodArg2, ...) {
      // ...
    })
  

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

  You can also intercept the method's incoming arguments via your middleware -- notice methodArg1, methodArg2, etc in the pre definition above. See section "Intercepting and mutating method arguments" below.

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

    .pre(method, true, function (next, done, methodArg1, methodArg2) {
      // ...
    })
  

  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...

myModel.save(function (err) {
  // err can come from a middleware
});

Intercepting and mutating method arguments

You can intercept method arguments via middleware.

For example, this would allow you to broadcast changes about your Documents every time someone sets a path in your Document to a new value:

schema.pre('set', function (next, path, val, typel) {
  // `this` is the current Document
  this.emit('set', path, val);

  // Pass control to the next pre
  next();
});

Moreover, you can mutate the incoming method arguments so that subsequent middleware see different values for those arguments. To do so, just pass the new values to next:

.pre(method, function firstPre (next, methodArg1, methodArg2) {
  // Mutate methodArg1
  next("altered-" + methodArg1.toString(), methodArg2);
})

// pre declaration is chainable
.pre(method, function secondPre (next, methodArg1, methodArg2) {
  console.log(methodArg1);
  // => 'altered-originalValOfMethodArg1' 
  
  console.log(methodArg2);
  // => 'originalValOfMethodArg2' 
  
  // Passing no arguments to `next` automatically passes along the current argument values
  // i.e., the following `next()` is equivalent to `next(methodArg1, methodArg2)`
  // and also equivalent to, with the example method arg 
  // values, `next('altered-originalValOfMethodArg1', 'originalValOfMethodArg2')`
  next();
})

Schema gotcha

type, when used in a schema has special meaning within Mongoose. If your schema requires using type as a nested property you must use object notation:

new Schema({
    broken: { type: Boolean }
  , asset : {
        name: String
      , type: String // uh oh, it broke. asset will be interpreted as String
    }
});

new Schema({
    works: { type: Boolean }
  , asset : {
        name: String
      , type: { type: String } // works. asset is an object with a type property
    }
});

API docs

You can find the Dox generated API docs here.

Getting support

Please subscribe to the Google Groups mailing list.

Join #mongoosejs on freenode.

Driver access

The driver being used defaults to node-mongodb-native and is directly accessible through YourModel.collection. Note: using the driver directly bypasses all Mongoose power-tools like validation, getters, setters, hooks, etc.

Mongoose Plugins

Take a peek at the plugins page to see contributions from the community. Add your own!

Contributing to Mongoose

Cloning the repository

Make a fork of mongoose, then clone it in your computer. The v2.x branch contains the current stable release, and the master branch the next upcoming major release.

Guidelines

• 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 specific 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.

Credits

• Guillermo Rauch - guillermo@learnboost.com - Guille
• Nathan White - nw
• Brian Noguchi - bnoguchi
• Aaron Heckmann - aheckmann

License

Copyright (c) 2010-2012 LearnBoost <dev@learnboost.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.