Cast to ObjectId failed for value "comments" at path "_id" for model "post" - mongodb

Question

Comments is an array nested inside Post Schema. I want to update corresponding post by push a new comment to the comments array. But got the error: CastError: Cast to ObjectId failed for value "comments" at path "_id" for model "post"
Read related posts
Tried to use "mongoose.Types.ObjectId", didn't work
Mongoose version ^5.5.4
All the ID I am using here are valid
const PostSchema = new Schema({
...
comments: [
{
user: {
type: Schema.Types.ObjectId,
ref: 'user',
},
body: {
type: String,
required: [true, 'Content required'],
},
}
],
...
});
PostRouter.put('/posts/comments', (req, res) => {
const { id } = req.query;
const userID = req.body.user;
const body = req.body.body;
const comment = {
user: userID,
body: body,
};
Posts
.update({ _id: id }, { $push: { comments: comment }})
.then(result => {
res.status(200).json(result.ok);
})
.catch(err => console.log(err));
});
I have a similar one: add a "friendID" to User Modal "friends" array. works as expected.
const senderID = req.query.sender;
const recipientID = req.query.recipient;
Users .update({ _id: recipientID }, { $push: { friends: senderID }})
.then(result => res.status(200).json(result.ok))
.catch(err => console.log(err));
but the "comment" I try to add here is an object instead of a valid ID string.
I think the problem is inside "Comments" array, because "comment.user" is ref from my "User" Schema. Don't know how to solve this nested question with cast error.

Answer 1

mongoose.Types.ObjectId is redundant if userID and _id are valid mongodb _id.
PostRouter.put('/posts/comments', (req, res) => {
const { id } = req.query;
const userID = req.body.user;
const body = req.body.body;
const comment = {
user: userID,
body: body,
};
Posts
.update({ _id: id }, { $push: { comments: comment }})
.then(result => {
res.status(200).json(result.ok);
})
.catch(err => console.log(err));
});