why Console.log(req.body.post) give correct id but using it in Post.findById return undefined

Question

When I am using req.body.post in Post.findById it gives undefined but when I use direct id in Post.findById it workes fine. Console.log(req.body.post) give correct id but using it in Post.findById gives undefined why undefined while console.log give correct id

const Post = require('../models/post');

module.exports.create = function(req,res){
    console.log(req.body.post);
    Post.findById(req.body.post,function(err,post){
        console.log(post);
        return res.redirect('/');
    })
}

Output
62175534d37c9ce165033cee 
undefined

when I use direct id which is console.log print then it works fine.

const Post = require('../models/post');

module.exports.create = function(req,res){
    console.log(req.body.post);
    Post.findById('62175534d37c9ce165033cee',function(err,post){
        console.log(post);
        return res.redirect('/');
    })
}

Output
{
  comment: [],
  _id: new ObjectId("62175534d37c9ce165033cee"),        
  content: 'sdf',
  user: new ObjectId("621749248e7de90faa6263d4"),       
  createdAt: 2022-02-24T09:51:48.621Z,
  updatedAt: 2022-02-24T09:51:48.621Z,
  __v: 0
}

It might just be how you've typed this into your question but you have a trailing space in the output from `console.log(req.body.post)`. Try `req.body.post.trim()` — Phil, Mar 08 '22 at 06:45
Check your frontend code then as that's where the extra space comes from — Phil, Mar 08 '22 at 06:48
but from where I am learning he use req.body.post and it worked — vishal singh, Mar 08 '22 at 06:48
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/242712/discussion-between-vishal-singh-and-phil). — vishal singh, Mar 08 '22 at 06:52

score 0 · Answer 1 · answered Mar 17 '22 at 20:33

console.log() output can sometimes be misleading, if you log an object expression. It may print a value that was not yet set at the time, when the code execution reached the console.log() statement (look here, for example: console.log() async or sync?)

To be on the safe side with your logging output, modify your code like this:

const Post = require('../models/post');

module.exports.create = function(req,res){
    const stringToLog = req.body.post;
    console.log(stringToLog);
    Post.findById(req.body.post,function(err,post){
        console.log(post);
        return res.redirect('/');
    })
}

Don't be surprised if this leads to a different result (or maybe it doesn't).

score -1 · Answer 2 · answered Mar 08 '22 at 06:42

-1

You need to import ObjectId from mongodb. Than you try to find id like next:

db.colection_name.find(ObjectId('621749248e7de90faa6263d4'))

As you see in your database, it's not just a simple string, it's an object.

ref: https://docs.mongodb.com/manual/reference/method/ObjectId/

answered Mar 08 '22 at 06:42

Aleksandar Biševac

29
3

Why does the string literal work then? – Phil Mar 08 '22 at 06:42
Given OP's code uses _models_, I'd say they're using [Mongoose](https://mongoosejs.com/docs/api.html#model_Model.findById) – Phil Mar 08 '22 at 06:46

why Console.log(req.body.post) give correct id but using it in Post.findById return undefined

2 Answers2