Firestore Store Date/Timestamp as UTC

I wanted to categorised my photos by day, thus each photo is given a day timestamp (in UTC) they belong to based on their local date.

• 21 February 2019 at 18:18:13 UTC+8 -> 2019-02-21
• 7 April 2019 at 11:34:32 UTC+12 -> 2019-04-07

Save to Database

val date = ... // LocalDateTime// remove time from dateval dayDate = date.truncatedTo(ChronoUnit.DAYS)// convert to UTC Timestamp for storageval timestamp = dayDate.toTimestamp(ZoneOffset.UTC)

NOTE: Refer to Covert LocalDateTime (java.time) to Firestore Timestamp

Read from Database

val timestamp = ...val dayDate = timestamp.toLocalDateTime(ZoneOffset.UTC)