Locate the generated ID of the inserted child when saving the parent in MongoDB

Question

Locate the generated ID of the inserted child when saving the parent in MongoDB

If I have a document representing a post with comments like the one below:

 {
    "_id": "579a2a71f7b5455c28a7abcb",
    "title": "post 1",
    "link": "www.link1.com",
    "__v": 0,
    "comments": [
      {
        "author": "Andy",
        "body": "Wish I had thought of that",
        "_id": "579a2a71f7b5455c28a7abcd",
        "upvotes": 0
      },
      {
        "author": "Jim",
        "body": "Just a comment",
        "_id": "579a2a71f7b5455c28a7abcc",
        "upvotes": 0
      }
    ],
    "upvotes": 5
  }

When adding a new comment in the javascript code by pushing to the post.comments array and saving the post using .save with a callback, how can I retrieve the newly generated _id of the comment saved?

Even though the parent post document is available in the callback, it doesn't indicate which specific comment was inserted.

Are there any other document methods or alternate forms of the .save callback that can address this situation?

Or should I resort to generating a unique id for the comment before saving, as I typically would?

EDITED: Using Mongoose, forgot to mention earlier!

javascript mongodb mongoose

Answer 1

Answer №1

Although you didn't explicitly state it, I assume that you are using Mongoose because the standard MongoDB does not automatically add an _id property to subdocuments.

The Mongoose documentation provides guidance on how to add sub-documents, with the following example code:

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

// create a comment
parent.children.push({ name: 'Liesl' });
var subdoc = parent.children[0];
console.log(subdoc) // { _id: '501d86090d371bab2c0341c5', name: 'Liesl' }
subdoc.isNew; // true

parent.save(function (err) {
  if (err) return handleError(err)
  console.log('Success!');
});

To access the inserted element, use

parent.children[parent.children.length - 1]

instead of parent.children[0].

Answer 2

Although you didn't explicitly state it, I assume that you are using Mongoose because the standard MongoDB does not automatically add an _id property to subdocuments.

The Mongoose documentation provides guidance on how to add sub-documents, with the following example code:

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

// create a comment
parent.children.push({ name: 'Liesl' });
var subdoc = parent.children[0];
console.log(subdoc) // { _id: '501d86090d371bab2c0341c5', name: 'Liesl' }
subdoc.isNew; // true

parent.save(function (err) {
  if (err) return handleError(err)
  console.log('Success!');
});

To access the inserted element, use

parent.children[parent.children.length - 1]

instead of parent.children[0].

Answer 3

Answer №2

In a scenario where multiple users are involved, relying on the last item pushed onto an array may not be a viable solution.

An alternative approach could involve comparing the author and comment fields, although this method may prove to be cumbersome and not always guarantee a match.

Another option would be to generate an object id and assign it to the comment before saving it, as demonstrated below:

var mongoose = require('mongoose'); 
var id = mongoose.Types.ObjectId();

Implementing this strategy should help resolve any potential issues.

Answer 4

In a scenario where multiple users are involved, relying on the last item pushed onto an array may not be a viable solution.

An alternative approach could involve comparing the author and comment fields, although this method may prove to be cumbersome and not always guarantee a match.

Another option would be to generate an object id and assign it to the comment before saving it, as demonstrated below:

var mongoose = require('mongoose'); 
var id = mongoose.Types.ObjectId();

Implementing this strategy should help resolve any potential issues.

Locate the generated ID of the inserted child when saving the parent in MongoDB

Answer №1

Answer №2

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