Mongoose embedded documents / DocumentsArrays id - node.js

Question

In the Mongoose documentation at the following address:
http://mongoosejs.com/docs/embedded-documents.html
There is a statement:
DocumentArrays have an special method id that filters your embedded
documents by their _id property (each embedded document gets one):
Consider the following snippet:
post.comments.id(my_id).remove();
post.save(function (err) {
// embedded comment with id `my_id` removed!
});
I've looked at the data and there are no _ids for the embedded documents as would appear to be confirmed by this post:
How to return the last push() embedded document
My question is:
Is the documentation correct? If so then how do I find out what 'my_id' is (in the example) to do a '.id(my_id)' in the first place?
If the documentation is incorrect is it safe to use the index as an id within the document array or should I generate a unique Id manually (as per the mentioned post).

Answer 1

Instead of doing push() with a json object like this (the way the mongoose docs suggest):
// create a comment
post.comments.push({ title: 'My comment' });
You should create an actual instance of your embedded object and push() that instead. Then you can grab the _id field from it directly, because mongoose sets it when the object is instantiated. Here's a full example:
var mongoose = require('mongoose')
var Schema = mongoose.Schema
var ObjectId = Schema.ObjectId
mongoose.connect('mongodb://localhost/testjs');
var Comment = new Schema({
title : String
, body : String
, date : Date
});
var BlogPost = new Schema({
author : ObjectId
, title : String
, body : String
, date : Date
, comments : [Comment]
, meta : {
votes : Number
, favs : Number
}
});
mongoose.model('Comment', Comment);
mongoose.model('BlogPost', BlogPost);
var BlogPost = mongoose.model('BlogPost');
var CommentModel = mongoose.model('Comment')
var post = new BlogPost();
// create a comment
var mycomment = new CommentModel();
mycomment.title = "blah"
console.log(mycomment._id) // <<<< This is what you're looking for
post.comments.push(mycomment);
post.save(function (err) {
if (!err) console.log('Success!');
})