$addToSet in a nested Array item - node.js

Question

Considering the following
User collection & sample User document
{
"_id" : ObjectId("575c01f7b8e5999addeb598c"),
"username" : "test.1#gmail.com",
"password" : "<password>",
"firstName" : "Test,
"lastName" : "User"
}
I am trying to run an update request to add an entry in userData.eventData which is meant to be an array
In mongo script I can do
> db.Users.update({_id: ObjectId("575c01f7b8e5999addeb598c")}, {"$addToSet":{"userData.eventData":"My event"}} )
And I have the following result : userData is created as an Object and eventData as a nested Array
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.Users.find({_id: ObjectId("575c01f7b8e5999addeb598c")})
{ "_id" : ObjectId("575c01f7b8e5999addeb598c"), "username" : "test.1#gmail.com", "password" : "<password>", "firstName" : "Test", "lastName" : "User", "userData" : { "eventData" : [ "My event" ] } }
While running the same logic in mongo (using driver version 2.1.21)
// with a properly initialized db object
db.collection("Users").update({"_id" : ObjectId("575c01f7b8e5999addeb598c")}, {"$addToSet": { "userData.eventData": "My Event"}}, function(err, result) {
// do something
});
I receive the following response
result:Object
n:0
nModified:0
ok:1
And indeed the database entry is unchanged.
Is that the way it is meant to behave? I can easily fix this by creating the userData.eventData array but I found disturbing the fact that node's Mongo driver and mongo shell didn't behave the same on this
Thanks in advance for your help & advice
Edit 13/6/16
Mistake was on my side, I missed a 'new' before 'ObjectId(...' in node. With it, it behaves exactly the same as in mongo shell (i.e. 'userData' is created as an Object and it includes 'eventData' array)
No issue, then :)

Answer 1

Update, updates an already existing object in your document.
What you want is insert or use upset which creates a new document when no document matches the query criteria
db.collection.update(
{ name: "Andy" },
{
name: "Andy",
rating: 1,
score: 1
},
{ upsert: true }
);
If you wanted to add an object to your array, you would need $push
// Insert a document in the capped collection
function push (db, collection, search, data, callback) {
db.collection(collection).update(
search, {
$push: data
}, function (err, result) {
console.log("New object pushed");
callback(err);
});
}