Delete object from array by given _id in in Mongoose

Question

In Mongoose model User given document look like this:

> db.users.find().pretty()
{
    /* ... */
    "events" : [
        {
            "_id" : ObjectId("537bb2faf87f9a552c3219ea"),
            "message" : "Foo"
        },
        {
            "_id" : ObjectId("537bb436c3b9a1aa2db71b7c"),
            "message" : "Bar"
        },
        {
            "_id" : ObjectId("537bb4ab2cc503e52e24d145"),
            "message" : "Biz"
        },
        {
            "_id" : ObjectId("537bb4d02cc503e52e24d146"),
            "message" : "Pop"
        }


]

}

Some function takes event _id as parameter and must delete object responding to this _id from MongoDB. I tried:

User
    .findByIdAndUpdate(req.user._id, {
        $pull: {events: {
            $elemMatch: {_id: _eventId}   //_eventId is string representation of event ID
        }}
    }, function(err) {
        // ...
    });

It is not working. What am I doing wrong?

Answer 1

Quote from SERVER-2016:

The argument to $pull is already applied to each element of the target array, so using $elemMatch is redundant in the update context.

So just execute your query without $elemMatch:

User
    .findByIdAndUpdate(req.user._id, {
        $pull: {events: {
            _id: _eventId   //_eventId is string representation of event ID
        }}
    }, function(err) {
        // ...
    });