Mongoose index on subdocument _id

subdocument-index.js

/*
I couldn't find an example of this anywhere, so here it is.
This example uses Mongoose 4, where objects in an array are given their own schema automatically.
*/
var mongoose = require("mongoose");
var mySchema = mongoose.Schema({
	name: String,
	things: [{
		_id: {auto: true, type: mongoose.Schema.ObjectId, index: true},
		name: String
	}]
});