Embedded Doc with _id

mongoose_use.js

var friend_schema = new mongoose.Schema({
    _id:mongoose.Schema.ObjectId,
    name:String
});

var person_schema = new mongoose.Schema({
    name:String,
    friends:[friend_schema]
});

var Person_Model = mongoose.Model('Person',  person_schema);

var person = new Person_Model({
            name:'Foo',
            friends:[
                {
                    name:'Bar'
                },
                {
                    name:'Sam'
                }
            ]
        });

person.save();

/**
 * friends have no ID -- they appear as entered.
 * { name: 'Foo',
  _id: 4fda6be639bba80000000001,
  friends: [ { name: 'Bar' }, { name: 'Sam' } ] }
*/