Conflict when updating a document with both $set and $currentDate - node.js

Question

I’m using Mongo 3.6.3 and I have a database with a collection and an item with _id equal to 1.
I want to update the item by adding an object and a timestamp inside of that object. However, I get an error. Here’s what I do:
function MyObject() {
this.bar = {
apples: 4,
bananas: 5
};
}
collection.update({
_id: 1
}, {
$set: {
"foo": new MyObject()
},
$currentDate: {
"foo.time": {
$type: 'timestamp'
}
}
}, function (err) {
console.log(err.name, err.message);
});
and I get:
MongoError Updating the path 'foo.time' would create a conflict at 'foo'
Why does that happen?
If I run the $set operation first and then the $currentDate one in another update(), I get the desired result:
{
"_id" : 1,
"foo" : {
"bar" : {
"apples" : 4,
"bananas" : 5
},
"time" : Timestamp(1523459420, 1)
}
}
However, if I try to do them simultaneously like I’ve shown in the code above, I get the error. Why?

Answer 1

You can't have multiple operators ($set and $currentDate) that modify the same path (foo in this case). In your case you could use dot notation though:
collection.update({
_id: 1
}, {
$set: {
"foo.bar.apples": 4,
"foo.bar.bananas": 5
},
$currentDate: {
"foo.time": {
$type: 'timestamp'
}
}
}, function (err) {
console.log(err.name, err.message);
});
or just change MyObject to set this.time = new Date() instead of using $currentDate.