MongoDB objectID stranger Error - node.js

Question

Using a MEAN Stack deployment on Heroku I am able to GET and DELETE Documents with mongoDB's findOne and deleteOne functions. However when I try to PUT a document with the mongoDB updateOne/update function, I receive this error (server side) :
The _id field cannot be changed from {_id: ObjectId('56d4d71191fdc81100974d0b')} to {_id: "56d4d71191fdc81100974d0b"}.
Seems strange because I am using the same method in my server code for updateOne as in findOne (again, findOne works fine):
app.get("/contacts/:id", function(req, res) {
db.collection(CONTACTS_COLLECTION).findOne({ _id: new ObjectID(req.params.id) }, function(err, doc) {
if (err) {
handleError(err.message, "Failed to get contact");
} else {
res.status(200).json(doc);
}
});
});
app.put("/contacts/:id", function(req, res) {
var updateDoc = req.body;
db.collection(CONTACTS_COLLECTION).updateOne({_id: new ObjectID(req.params.id)}, updateDoc, function(err, doc) {
if (err) {
handleError(err.message, "Failed to update contact");
} else {
res.status(204).end();
}
});
});
Any suggestions?

Answer 1

I think you have problem at var updateDoc = req.body
As req.body contains id field and you are searching from object to update by that id, mongodb thinks you are trying to update
id field too which is not allowed.
One solution is to remove id field from your updateDoc object.
e.g.
delete updateDoc._id;
now try again and see if it works.
Your final function should look like
app.put("/contacts/:id", function(req, res) {
var updateDoc = req.body;
delete updateDoc.id;
db.collection(CONTACTS_COLLECTION).updateOne({_id: new ObjectID(req.params.id)}, updateDoc, function(err, doc) {
if (err) {
handleError(err.message, "Failed to update contact");
} else {
res.status(204).end();
}
});
});