Mongoose saves in UTC but needs to retrieve in different timezones depends on the user timezone - express

Question

Mongoose saves all dates in UTC format that's OK.
Each user has a specific timezone. It stores the in user's document.
I would like to send any documents to the client with converted dates in the user's timezone.
I know how to format one value, but I'm looking for a solution to avoid transformation one-by-one.
The workaround solution will be a pass-through transform function on the client for each value or recursive modification response.
Any thoughts?

Answer 1

You can do this in aggregation.
Lets say you have this data:
[
{
"_id": {
"$oid": "5f18b5c87f9f9c0fd8322b60"
},
"createdAt": {
"$date": "2020-07-22T21:55:20.575Z"
},
},
{
"_id": {
"$oid": "5f19efac5cfa75483865eaa2"
},
"createdAt": {
"$date": "2020-07-23T20:14:36.108Z"
},
}
]
you can do this:
const timezone = "America/Chicago"
Model.aggregate([
{
$set: {
localTime: {
$dateToString: {
date: "$createdAt",
timezone
}
}
},
}
]);
The result of the aggregation will be:
[
{
"_id": ObjectId("5f18b5c87f9f9c0fd8322b60"),
"createdAt": ISODate("2020-07-22T21:55:20.575Z"),
"localTime": "2020-07-22T16:55:20.575Z"
},
{
"_id": ObjectId("5f19efac5cfa75483865eaa2"),
"createdAt": ISODate("2020-07-23T20:14:36.108Z"),
"localTime": "2020-07-23T15:14:36.108Z"
}
]
Demo example: https://mongoplayground.net/p/7IOGMrC2sf5