Upserting nested fields with a dot(.) in key in MongoDB - mongodb

Question

I have query in MongoDB for which I'm trying to upsert an inner nested attribute that contains a dot(.) in the key. E.g. a document might look something like: (below is a fictitious example just to highlight the constraint I'm facing.)
const person = {
name: 'Peter',
address: {
'NY.postalCode': 12345,
'CA.postalCode': 23456,
}
}
However, when I try to update one of the nested attribute in address with the below $set operation, I get an additional object NY under address and its subKey postalCode as a result, instead of the flattened attribute within address.
await Person.findByIdAndUpdate(id, {
$set: {
'address.NY.postalCode': 98765,
}
}, { new: true });
// Output
{
name: 'Peter',
address: {
'NY.postalCode': 12345,
'CA.postalCode': 23456,
NY: {
postalCode: 98765,
}
}
}
I've tried using the escape character for dot (\u002e), but get the same output. Also, I have seen some new features for setting fields but only in Mongo v5: https://www.mongodb.com/docs/manual/reference/operator/aggregation/setField/#mongodb-expression-exp.-setField. However, we're using Mongo v4.2 and would not be able to upgrade until a while later.
Would like to check if there are any means to $set nested attributes in address that don't completely replace the address object? i.e. to be able to specifically upsert an inner attribute within address object?
For example, is it possible to use the aggregation framework to workaround this?
I've tried something like the below, but it didn't work - not sure if its something that I did wrong or its probably not possible to use the aggregation pipeline..
Person.aggregate([
{
$match: {
_id: id,
},
},
{
$replaceRoot: { newRoot: {
$mergeObjects: [
'$$ROOT.address',
{
'NY.postalCode': 98765,
},
],
} },
},
]);

Answer 1

For your scenario, you need to achieve the update with aggregation pipeline.
Use $literal to escape the field name with dot.
Via $mergeObjects to merge current address object with { NY.postalCode': 98765 }.
db.collection.update({
"_id": ObjectId("5a934e000102030405000000")
},
[
{
$set: {
"address": {
$mergeObjects: [
"$address",
{
$literal: {
"NY.postalCode": 98765
}
}
]
}
}
}
],
{
new: true
})
Demo # Mongo Playground