Mongoose update object in an embedded array

Question

I want to update a comment in a post. I first retrieve the post document which looks like this.

{
    "_id" : ObjectId("5aac169c229f0136296407d4"),
    "title" : "First Node.js App",
    "body" : "testing 123",
    "status" : "public",
    "user" : "John Doe",
    "date" : ISODate("2017-12-21T18:30:09.779Z"),
    "comments" : [ 
        {
            "commentBody" : "This is awesome! ",
            "commentUser" : ObjectId("5a3bfd5a9e65351f9c18ba18"),
            "_id" : ObjectId("5a3c02379e65351f9c18ba1a"),
            "commentDate" : ISODate("2017-12-21T18:49:27.620Z")
        },
        {
            "commentBody" : "This is second comment.",
            "commentUser" : ObjectId("5a3bfd5a9e65351f9c18gt19"),
            "_id" : ObjectId("5a3c02379e65351f9c18ba1b"),
            "commentDate" : ISODate("2017-12-21T18:49:27.620Z")
        }
    ],
    "allowComments" : true
}

Let say I want to update comment with "_id" ObjectId("5a3c02379e65351f9c18ba1a").

I've tried the following without luck.

const post = await Post.findById(req.body.postID);

await post.update({'comments._id' : req.body.commentID},{$set : {
  'comments.$.commentBody': req.body.comment
  }
});

This gave me the following error: MongoError: cannot use the part (comments of comments._id) to traverse the element

Any suggestion would be greatly appreciated. Thanks in advance!

score 1 · Accepted Answer · edited Apr 02 '18 at 19:37

1

You can try something like this::

Post.findOneAndUpdate(
{ "_id": req.body.postID, "comments._id": req.body.commentID },
    { 
        "$set": {
            'comments.$.commentBody': req.body.comment
        }
    },
    function(err,doc) {

    }
);

edited Apr 02 '18 at 19:37

user752746

617
9
31

answered Apr 02 '18 at 18:41

Akshansh Thakur

5,163
2
21
38

This might not get you the correct answer line by line.. this is just an idea. I'm a little new to node myself – Akshansh Thakur Apr 02 '18 at 18:42
Hi Akshansh, thank you for your suggestion. I'm getting the following error: The positional operator did not find the match needed from the query. Don't you have to include the comment id "ObjectId("5a3c02379e65351f9c18ba1a")" you want to update somewhere? – user752746 Apr 02 '18 at 19:12
@user752746 .. check this out https://stackoverflow.com/questions/26156687/mongoose-find-update-subdocument – Akshansh Thakur Apr 02 '18 at 19:13
Thank you very much Akshansh, that link was very helpful. I'm able to update my comment now. – user752746 Apr 02 '18 at 19:23
I added ("comments._id": req.body.commentID) to your suggestion and it worked. – user752746 Apr 02 '18 at 19:38
happy! coding :)\ – Akshansh Thakur Apr 02 '18 at 19:39

score 0 · Answer 2 · answered Apr 02 '18 at 19:21

I'm not sure about how to implement this in node.js but here is the Mongo query:

db.sample.aggregate([
{$match:{"comments.commentUser":ObjectId("5a3bfd5a9e65351f9c18ba19")}},
{$redact:{
     $cond:{
       if:{$or:[{$eq:["$commentUser",ObjectId("5a3bfd5a9e65351f9c18ba19")]}, 
{$not:"$commentUser"}]},
     then:"$$DESCEND",
     else:"$$PRUNE"
    }

}},
  {$addFields:{comments:{$map:{
                     input:"$comments",
                     as:"comment",
                     in:{"commentBody":"test comment", "commentUser" : "$$comment.commentUser", "_id" :"$$comment._id", "commentDate" :"$$comment.commentDate"}

    }}

   }},
   {$out:"sample"} 
])

Restricted the document such that only particular user id comments are displayed. After that, added comments with updated comment. Finally replacing the original content within aggregation without update query(note that collection will get replaced if you run the query). I didnt test this extensively, but working for small data set in my local. However, you might need to add some tweaks to this query and then check how u can add same query to node.js

Mongoose update object in an embedded array

2 Answers2