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Sub Docs

Sub-documents are docs with schemas of their own which are elements of a parents document array:

var childSchema = new Schema({ name: 'string' });

var parentSchema = new Schema({
  children: [childSchema]

Sub-documents enjoy all the same features as normal documents. The only difference is that they are not saved individually, they are saved whenever their top-level parent document is saved.

var Parent = db.model('Parent', parentSchema);
var parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
parent.children[0].name = 'Matthew';;

If an error occurs in a sub-documents' middleware, it is bubbled up to the save() callback of the parent, so error handling is a snap!

childSchema.pre('save', function (next) {
  if ('invalid' == return next(new Error('#sadpanda'));

var parent = new Parent({ children: [{ name: 'invalid' }] }); (err) {
  console.log(err.message) // #sadpanda

Finding a sub-document

Each document has an _id. DocumentArrays have a special id method for looking up a document by its _id.

var doc =;

Adding sub-docs

MongooseArray methods such as push, unshift, addToSet, and others cast arguments to their proper types transparently:

var Parent = db.model('Parent');
var parent = new Parent;

// create a comment
post.children.push({ name: 'Liesl' });
var doc = post.children[0];
console.log(doc) // { _id: '501d86090d371bab2c0341c5', name: 'Liesl' }
doc.isNew; // true (err) {
  if (err) return handleError(err)

Sub-docs may also be created without adding them to the array by using the create method of MongooseArrays.

var newdoc = post.children.create({ name: 'Aaron' });

Removing docs

Each sub-document has it's own remove method.

var doc =; (err) {
  if (err) return handleError(err);
  console.log('the sub-doc was removed')

Alternate declaration syntax

New in v3 If you don't need access to the sub-document schema instance, you may also declare sub-docs by simply passing an object literal:

var parentSchema = new Schema({
  children: [{ name: 'string' }]

Next Up

Now that we've covered Sub-documents, let's take a look at querying.