Mongoose Embedding Sub-Documents

  node.js, question
const EventSchema = new Schema({
 dates: [Number],
 reason: {
 type: String,
 required: true
 },
 userId: Schema.Types.ObjectId,
 type: {
 type: String,
 required: true
 bracket
 });
const CalendarSchema = new Schema({
 date: {
 type: Number,
 index: {
 unique: true
 bracket
 },
 events: [EventSchema]
 });

Is it okay to embed subdocuments like this in mongoose? But I made a mistake when inserting the subdocument.

.post(({ body }, res, next) => {
 const event = new Event(body);
 event.save()
 .then(savedEvent => {
 let promises = [];
 for (date of body.dates) {
 promises.push(Calendar.update({date}, {
 $push: savedEvent._doc
 }));
 bracket
 return Promise.all(promises);
 })
 .then(() => res.end())
 .catch(next);
 })

Error:
The field ‘_id’ must be an array but is of type OID in document {_id: ObjectId(’57c5a02c8890a02814771df1′)}

Did I write something wrong?

Isn’t the writing quite right? It’s used in the document
var personSchema = Schema({
_id : Number,
name : String,
age : Number,
stories : [{ type: Schema.Types.ObjectId, ref: ‘Story’ }]
});
var storySchema = Schema({
_creator : { type: Number, ref: ‘Person’ },
title : String,
fans : [{ type: Number, ref: ‘Person’ }]
});