Mongoose pull ObjectId from array - mongodb

Question

i'm trying to do a pretty simple operation, pull an item from an array with Mongoose on a Mongo database like so:
User.update({ _id: fromUserId }, { $pull: { linkedUsers: [idToDelete] } });
fromUserId & idToDelete are both Objects Ids.
The schema for Users goes like this:
var UserSchema = new Schema({
groups: [],
linkedUsers: [],
name: { type: String, required: true, index: { unique: true } }
});
linkedUsers is an array that only receives Ids of other users.
I've tried this as well:
User.findOne({ _id: fromUserId }, function(err, user) {
user.linkedUsers.pull(idToDelete);
user.save();
});
But with no luck.
The second option seem to almost work when i console the lenghts of the array at different positions but after calling save and checking, the length is still at 36:
User.findOne({ _id: fromUserId }, function(err, user) {
console.log(user.linkedUsers.length); // returns 36
user.linkedUsers.pull(idToDelete);
console.log(user.linkedUsers.length); // returns 35
user.save();
});
So it looks like i'm close but still, no luck. Both Ids are sent via the frontend side of the app.
I'm running those versions:
"mongodb": "^2.2.29",
"mongoose": "^5.0.7",
Thanks in advance.

Answer 1

You need to explicitly define the types in your schema definition i.e.
groups: [{ type: Schema.Types.ObjectId, ref: 'Group' }],
linkedUsers: [{ type: Schema.Types.ObjectId, ref: 'User' }]
and then use either
User.findOneAndUpdate(
{ _id: fromUserId },
{ $pullAll: { linkedUsers: [idToDelete] } },
{ new: true },
function(err, data) {}
);
or
User.findByIdAndUpdate(fromUserId,
{ $pullAll: { linkedUsers: [idToDelete] } },
{ new: true },
function(err, data) {}
);

Answer 2

I had a similar issue. I wanted to delete an object from an array, using the default _id from mongo, but my query was wrong:
const update = { $pull: { cities: cityId }};
It should be:
const update = { $pull: { cities: {_id: cityId} }};