Documentation
The official documentation website is mongoosejs.com.
Mongoose 8.0.0 was released on October 31, 2023. You can find more details on backwards breaking changes in 8.0.0 on our docs site.
Plugins
Check out the plugins search site to see hundreds of related modules from the community. Next, learn how to write your own plugin from the docs or this blog post.
Overview
Connecting to MongoDB
First, we need to define a connection. If your app uses only one database, you should use mongoose.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.
await mongoose.connect('mongodb://127.0.0.1/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.
Note: If the local connection fails then try using 127.0.0.1 instead of localhost. Sometimes issues may arise when the local hostname has been changed.
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.
const Schema = mongoose.Schema;
const ObjectId = Schema.ObjectId;
const 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
- pseudo-JOINs
The following example shows some of these features:
const 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/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
const MyModel = mongoose.model('ModelName');
Or just do it all at once
const MyModel = mongoose.model('ModelName', mySchema);
The first argument is the singular name of the collection your model is for. Mongoose automatically looks for the plural version of your model name. For example, if you use
const MyModel = mongoose.model('Ticket', mySchema);
Then MyModel will use the tickets collection, not the ticket collection. For more details read the model docs.
Once we have our model, we can then instantiate it, and save it:
const instance = new MyModel();
instance.my.key = 'hello';
await instance.save();
Or we can find documents from the same collection
await MyModel.find({});
You can also findOne, findById, update, etc.
const instance = await MyModel.findOne({ /* ... */ });
console.log(instance.my.key); // 'hello'
For more details check out the docs.
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:
const conn = mongoose.createConnection('your connection string');
const MyModel = conn.model('ModelName', schema);
const m = new MyModel();
await m.save(); // works
vs
const conn = mongoose.createConnection('your connection string');
const MyModel = mongoose.model('ModelName', schema);
const m = new MyModel();
await 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: [Comment]
Where Comment is a Schema we created. This means that creating embedded documents is as simple as:
// retrieve my model
const BlogPost = mongoose.model('BlogPost');
// create a blog post
const post = new BlogPost();
// create a comment
post.comments.push({ title: 'My comment' });
await post.save();
The same goes for removing them:
const post = await BlogPost.findById(myId);
post.comments[0].deleteOne();
await post.save();
Embedded documents enjoy all the same features as your models. Defaults, validators, middleware.
Middleware
See the docs page.
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:
schema.pre(method, function firstPre(next, methodArg1, methodArg2) {
// Mutate methodArg1
next('altered-' + methodArg1.toString(), methodArg2);
});
// pre declaration is chainable
schema.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
}
});
Driver Access
Mongoose is built on top of the official MongoDB Node.js driver. Each mongoose model keeps a reference to a native MongoDB driver collection. The collection object can be accessed using YourModel.collection. However, using the collection object directly bypasses all mongoose features, including hooks, validation, etc. The one
notable exception that YourModel.collection still buffers
commands. As such, YourModel.collection.find() will not
return a cursor.
API Docs
Find the API docs here, generated using dox and acquit.