mongoose

What is mongoose?

Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node.js. It manages relationships between data, provides schema validation, and is used to translate between objects in code and the representation of those objects in MongoDB.

What are mongoose's main functionalities?

Schema Definition

Defines a schema for a collection with various field types, validation, and defaults.

{"const mongoose = require('mongoose');\nconst Schema = mongoose.Schema;\nconst blogSchema = new Schema({\n  title: String,\n  author: String,\n  body: String,\n  comments: [{ body: String, date: Date }],\n  date: { type: Date, default: Date.now },\n  hidden: Boolean,\n  meta: {\n    votes: Number,\n    favs: Number\n  }\n});"}

Model Creation

Creates a model based on a defined schema, which can then be used to create, read, update, and delete documents of that schema type.

{"const mongoose = require('mongoose');\nconst Blog = mongoose.model('Blog', blogSchema);"}

Connection to MongoDB

Establishes a connection to a MongoDB database.

{"const mongoose = require('mongoose');\nmongoose.connect('mongodb://localhost/my_database', {useNewUrlParser: true, useUnifiedTopology: true});"}

Querying

Queries the database for documents matching certain criteria.

{"Blog.find({ author: 'John Doe' }).exec((err, blogs) => {\n  if (err) return handleError(err);\n  console.log('The blogs are', blogs);\n});"}

Data Validation

Ensures that the data being saved to the database meets certain criteria defined in the schema.

{"const personSchema = new Schema({\n  name: {\n    type: String,\n    required: true\n  },\n  age: {\n    type: Number,\n    min: 18,\n    max: 65\n  }\n});"}

Middleware (Hooks)

Allows execution of code before or after certain actions, such as saving a document.

{"blogSchema.pre('save', function(next) {\n  if (!this.isModified('title')) {\n    return next();\n  }\n  this.modifiedAt = Date.now();\n  next();\n});"}

Other packages similar to mongoose

sequelize

Sequelize is a promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication and more. Unlike Mongoose, which is designed for MongoDB, Sequelize is used for relational databases.

typeorm

TypeORM is an ORM that can run in Node.js and be used with TypeScript and JavaScript (ES5, ES6, ES7, ES8). It supports both Active Record and Data Mapper patterns, unlike Mongoose which is primarily schema-based. TypeORM works with SQL databases like MySQL, PostgreSQL, and SQLite.

waterline

Waterline is a data store-agnostic ORM that is bundled in the Sails.js framework but can also be used separately. It provides a uniform API for accessing different kinds of databases, including both SQL and NoSQL, and thus offers more flexibility compared to Mongoose which is MongoDB-specific.

bookshelf

Bookshelf is a JavaScript ORM for Node.js, built on the Knex SQL query builder. It features both promise-based and traditional callback interfaces, transaction support, and eager/nested-eager relation loading. Bookshelf is designed for relational databases and thus is a different choice compared to Mongoose for MongoDB.

README

Mongoose 1.0

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 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);

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 [e-mail]:LearnBoost/mongoose.git support/mongoose/

// in your code
require.paths.unshift('support/mongoose/lib')

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.

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

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 }
});

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

// 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 (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();
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 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' });

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 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:

• 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();
})

API docs

You can find the Dox generated API docs at http://mongoosejs.com.

Getting support

Please subscribe to the Google Groups mailing list.

Mongoose Plugins

The following plugins are currently available for use with mongoose:

• mongoose-types - Adds several additional types (e.g., Email) that you can use in your Schema declarations
• mongoose-auth - A drop in solution for your auth needs. Currently supports Password, Facebook, Twitter, Github, and more.
• mongoose-dbref - Adds DBRef support
• mongoose-joins - Adds simple join support

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).

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 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.

Credits

• Guillermo Rauch - [e-mail] - Guille
• Nathan White - nw
• Brian Noguchi - bnoguchi
• Aaron Heckmann - aheckmann

License

Copyright (c) 2010 LearnBoost <[e-mail]>

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.