SchemaTypes handle definition of path defaults, validation, getters, setters, field selection defaults for queries, and other general characteristics for Mongoose document properties.

You can think of a Mongoose schema as the configuration object for a Mongoose model. A SchemaType is then a configuration object for an individual property. A SchemaType says what type a given path should have, whether it has any getters/setters, and what values are valid for that path.

const schema = new Schema({ name: String });
schema.path('name') instanceof mongoose.SchemaType; // true
schema.path('name') instanceof mongoose.Schema.Types.String; // true
schema.path('name').instance; // 'String'

A SchemaType is different from a type. In other words, mongoose.ObjectId !== mongoose.Types.ObjectId. A SchemaType is just a configuration object for Mongoose. An instance of the mongoose.ObjectId SchemaType doesn't actually create MongoDB ObjectIds, it is just a configuration for a path in a schema.

The following are all the valid SchemaTypes in Mongoose. Mongoose plugins can also add custom SchemaTypes like int32. Check out Mongoose's plugins search to find plugins.


var schema = new Schema({
  name:    String,
  binary:  Buffer,
  living:  Boolean,
  updated: { type: Date, default: },
  age:     { type: Number, min: 18, max: 65 },
  mixed:   Schema.Types.Mixed,
  _someId: Schema.Types.ObjectId,
  decimal: Schema.Types.Decimal128,
  array: [],
  ofString: [String],
  ofNumber: [Number],
  ofDates: [Date],
  ofBuffer: [Buffer],
  ofBoolean: [Boolean],
  ofMixed: [Schema.Types.Mixed],
  ofObjectId: [Schema.Types.ObjectId],
  ofArrays: [[]],
  ofArrayOfNumbers: [[Number]],
  nested: {
    stuff: { type: String, lowercase: true, trim: true }
  map: Map,
  mapOfString: {
    type: Map,
    of: String

// example use

var Thing = mongoose.model('Thing', schema);

var m = new Thing; = 'Statue of Liberty';
m.age = 125;
m.updated = new Date;
m.binary = Buffer.alloc(0); = false;
m.mixed = { any: { thing: 'i want' } };
m._someId = new mongoose.Types.ObjectId;
m.ofDates.addToSet(new Date);
m.ofMixed = [1, [], 'three', { four: 5 }];
m.nested.stuff = 'good'; = new Map([['key', 'value']]);;

SchemaType Options

You can declare a schema type using the type directly, or an object with a type property.

var schema1 = new Schema({
  test: String // `test` is a path of type String

var schema2 = new Schema({
  // The `test` object contains the "SchemaType options"
  test: { type: String } // `test` is a path of type string

In addition to the type property, you can specify additional properties for a path. For example, if you want to lowercase a string before saving:

var schema2 = new Schema({
  test: {
    type: String,
    lowercase: true // Always convert `test` to lowercase

You can add any property you want to your SchemaType options. Many plugins rely on custom SchemaType options. For example, the mongoose-autopopulate plugin automatically populates paths if you set autopopulate: true in your SchemaType options. Mongoose comes with support for several built-in SchemaType options, like lowercase in the above example.

The lowercase option only works for strings. There are certain options which apply for all schema types, and some that apply for specific schema types.

All Schema Types
  • required: boolean or function, if true adds a required validator for this property
  • default: Any or function, sets a default value for the path. If the value is a function, the return value of the function is used as the default.
  • select: boolean, specifies default projections for queries
  • validate: function, adds a validator function for this property
  • get: function, defines a custom getter for this property using Object.defineProperty().
  • set: function, defines a custom setter for this property using Object.defineProperty().
  • alias: string, mongoose >= 4.10.0 only. Defines a virtual with the given name that gets/sets this path.
var numberSchema = new Schema({
  integerOnly: {
    type: Number,
    get: v => Math.round(v),
    set: v => Math.round(v),
    alias: 'i'

var Number = mongoose.model('Number', numberSchema);

var doc = new Number();
doc.integerOnly = 2.001;
doc.integerOnly; // 2
doc.i; // 2
doc.i = 3.001;
doc.integerOnly; // 3
doc.i; // 3

You can also define MongoDB indexes using schema type options.

  • index: boolean, whether to define an index on this property.
  • unique: boolean, whether to define a unique index on this property.
  • sparse: boolean, whether to define a sparse index on this property.
var schema2 = new Schema({
  test: {
    type: String,
    index: true,
    unique: true // Unique index. If you specify `unique: true`
    // specifying `index: true` is optional if you do `unique: true`
  • lowercase: boolean, whether to always call .toLowerCase() on the value
  • uppercase: boolean, whether to always call .toUpperCase() on the value
  • trim: boolean, whether to always call .trim() on the value
  • match: RegExp, creates a validator that checks if the value matches the given regular expression
  • enum: Array, creates a validator that checks if the value is in the given array.
  • minlength: Number, creates a validator that checks if the value length is not less than the given number
  • maxlength: Number, creates a validator that checks if the value length is not greater than the given number
  • min: Number, creates a validator that checks if the value is greater than or equal to the given minimum.
  • max: Number, creates a validator that checks if the value is less than or equal to the given maximum.
  • min: Date
  • max: Date

Usage notes


To declare a path as a string, you may use either the String global constructor or the string 'String'.

const schema1 = new Schema({ name: String }); // name will be cast to string
const schema2 = new Schema({ name: 'String' }); // Equivalent

const Person = mongoose.model('Person', schema2);

If you pass an element that has a toString() function, Mongoose will call it, unless the toString() function is strictly equal to Object.prototype.toString().

new Person({ name: 42 }).name; // "42" as a string
new Person({ name: { toString: () => 42 } }).name; // "42" as a string

// "undefined", will get a cast error if you `save()` this document 
new Person({ name: { foo: 42 } }).name;


To declare a path as a number, you may use either the Number global constructor or the string 'Number'.

const schema1 = new Schema({ age: Number }); // age will be cast to a Number
const schema2 = new Schema({ age: 'Number' }); // Equivalent

const Car = mongoose.model('Car', schema2);

There are several types of values that will be successfully cast to a Number.

new Car({ age: '15' }).age; // 15 as a Number
new Car({ age: true }).age; // 1 as a Number
new Car({ age: false }).age; // 0 as a Number
new Car({ age: { valueOf: () => 83 } }).age; // 83 as a Number

If you pass an object with a valueOf() function that returns a Number, Mongoose will call it and assign the returned value to the path.

The values null and undefined are not cast.

NaN, strings that cast to NaN, arrays, and objects that don't have a valueOf() function will all result in a CastError.


Built-in Date methods are not hooked into the mongoose change tracking logic which in English means that if you use a Date in your document and modify it with a method like setMonth(), mongoose will be unaware of this change and will not persist this modification. If you must modify Date types using built-in methods, tell mongoose about the change with doc.markModified('pathToYourDate') before saving.

var Assignment = mongoose.model('Assignment', { dueDate: Date });
Assignment.findOne(function (err, doc) {
  doc.dueDate.setMonth(3);; // THIS DOES NOT SAVE YOUR CHANGE

  doc.markModified('dueDate');; // works


To declare a path as a Buffer, you may use either the Buffer global constructor or the string 'Buffer'.

const schema1 = new Schema({ binData: Buffer }); // binData will be cast to a Buffer
const schema2 = new Schema({ binData: 'Buffer' }); // Equivalent

const Data = mongoose.model('Data', schema2);

Mongoose will successfully cast the below values to buffers.

const file1 = new Data({ binData: 'test'}); // {"type":"Buffer","data":[116,101,115,116]}
const file2 = new Data({ binData: 72987 }); // {"type":"Buffer","data":[27]}
const file4 = new Data({ binData: { type: 'Buffer', data: [1, 2, 3]}}); // {"type":"Buffer","data":[1,2,3]}


An "anything goes" SchemaType. Mongoose will not do any casting on mixed paths. You can define a mixed path using Schema.Types.Mixed or by passing an empty object literal. The following are equivalent.

const Any = new Schema({ any: {} });
const Any = new Schema({ any: Object });
const Any = new Schema({ any: Schema.Types.Mixed });
const Any = new Schema({ any: mongoose.Mixed });
// Note that if you're using `type`, putting _any_ POJO as the `type` will
// make the path mixed.
const Any = new Schema({
  any: {
    type: { foo: String }

Since it is a schema-less type, you can change the value to anything else you like, but Mongoose loses the ability to auto detect and save those changes. To tell Mongoose that the value of a Mixed type has changed, you need to call doc.markModified(path), passing the path to the Mixed type you just changed.

person.anything = { x: [3, 4, { y: "changed" }] };
person.markModified('anything');; // Mongoose will save changes to `anything`.


To specify a type of ObjectId, use Schema.Types.ObjectId in your declaration.

var mongoose = require('mongoose');
var ObjectId = mongoose.Schema.Types.ObjectId;
var Car = new Schema({ driver: ObjectId });
// or just Schema.ObjectId for backwards compatibility with v2


Booleans in Mongoose are plain JavaScript booleans. By default, Mongoose casts the below values to true:

  • true
  • 'true'
  • 1
  • '1'
  • 'yes'

Mongoose casts the below values to false:

  • false
  • 'false'
  • 0
  • '0'
  • 'no'

Any other value causes a CastError. You can modify what values Mongoose converts to true or false using the convertToTrue and convertToFalse properties, which are JavaScript sets.

const M = mongoose.model('Test', new Schema({ b: Boolean }));
console.log(new M({ b: 'nay' }).b); // undefined

// Set { false, 'false', 0, '0', 'no' }

console.log(new M({ b: 'nay' }).b); // false


Mongoose supports arrays of SchemaTypes and arrays of subdocuments. Arrays of SchemaTypes are also called primitive arrays, and arrays of subdocuments are also called document arrays.

var ToySchema = new Schema({ name: String });
var ToyBoxSchema = new Schema({
  toys: [ToySchema],
  buffers: [Buffer],
  strings: [String],
  numbers: [Number]
  // ... etc

Arrays are special because they implicitly have a default value of [] (empty array).

var ToyBox = mongoose.model('ToyBox', ToyBoxSchema);
console.log((new ToyBox()).toys); // []

To overwrite this default, you need to set the default value to undefined

var ToyBoxSchema = new Schema({
  toys: {
    type: [ToySchema],
    default: undefined

Note: specifying an empty array is equivalent to Mixed. The following all create arrays of Mixed:

var Empty1 = new Schema({ any: [] });
var Empty2 = new Schema({ any: Array });
var Empty3 = new Schema({ any: [Schema.Types.Mixed] });
var Empty4 = new Schema({ any: [{}] });


New in Mongoose 5.1.0

A MongooseMap is a subclass of the built-in Map class. In these docs, we'll use the terms 'map' and MongooseMap interchangeably. In Mongoose, maps are how you create a nested document with arbitrary keys.

Note: In Mongoose Maps, keys must be strings in order to store the document in MongoDB.

const userSchema = new Schema({
  // `socialMediaHandles` is a map whose values are strings. A map's
  // keys are always strings. You specify the type of values using `of`.
  socialMediaHandles: {
    type: Map,
    of: String

const User = mongoose.model('User', userSchema);
// Map { 'github' => 'vkarpov15', 'twitter' => '@code_barbarian' }
console.log(new User({
  socialMediaHandles: {
    github: 'vkarpov15',
    twitter: '@code_barbarian'

The above example doesn't explicitly declare github or twitter as paths, but, since socialMediaHandles is a map, you can store arbitrary key/value pairs. However, since socialMediaHandles is a map, you must use .get() to get the value of a key and .set() to set the value of a key.

const user = new User({
  socialMediaHandles: {}

// Good
user.socialMediaHandles.set('github', 'vkarpov15');
// Works too
user.set('socialMediaHandles.twitter', '@code_barbarian');
// Bad, the `myspace` property will **not** get saved
user.socialMediaHandles.myspace = 'fail';

// 'vkarpov15'
// '@code_barbarian'
// undefined

// Will only save the 'github' and 'twitter' properties;

Map types are stored as BSON objects in MongoDB. Keys in a BSON object are ordered, so this means the insertion order property of maps is maintained.


Getters are like virtuals for paths defined in your schema. For example, let's say you wanted to store user profile pictures as relative paths and then add the hostname in your application. Below is how you would structure your userSchema:

const root = '';

const userSchema = new Schema({
  name: String,
  picture: {
    type: String,
    get: v => `${root}${v}`

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

const doc = new User({ name: 'Val', picture: '/123.png' });
doc.picture; // ''
doc.toObject({ getters: false }).picture; // '123.png'

Generally, you only use getters on primitive paths as opposed to arrays or subdocuments. Because getters override what accessing a Mongoose path returns, declaring a getter on an object may remove Mongoose change tracking for that path.

const schema = new Schema({
  arr: [{ url: String }]

const root = '';

// Bad, don't do this!
schema.path('arr').get(v => {
  return => Object.assign(el, { url: root + el.url }));

// Later
doc.arr.push({ key: String });
doc.arr[0]; // 'undefined' because every `doc.arr` creates a new array!

Instead of declaring a getter on the array as shown above, you should declare a getter on the url string as shown below. If you need to declare a getter on a nested document or array, be very careful!

const schema = new Schema({
  arr: [{ url: String }]

const root = '';

// Good, do this instead of declaring a getter on `arr`
schema.path('arr.0.url').get(v => `${root}${v}`);

Creating Custom Types

Mongoose can also be extended with custom SchemaTypes. Search the plugins site for compatible types like mongoose-long, mongoose-int32, and other types.

The schema.path() Function

The schema.path() function returns the instantiated schema type for a given path.

var sampleSchema = new Schema({ name: { type: String, required: true } });
// Output looks like:
 * SchemaString {
 *   enumValues: [],
 *   regExp: null,
 *   path: 'name',
 *   instance: 'String',
 *   validators: ...

You can use this function to inspect the schema type for a given path, including what validators it has and what the type is.

Next Up

Now that we've covered SchemaTypes, let's take a look at Connections.