How to aggregate by year-month-day on a different timezone

Question

I have a MongoDB whom store the date objects in UTC. Well, I want to perform aggregation by year,month day in a different timezone (CET).

doing this, works fine for

Answer 1

MongoDB's documentation suggests that you save the timezone offset alongside the timestamp:

var now = new Date();
db.data.save( { date: now,
                offset: now.getTimezoneOffset() } );

This is of course not the ideal solution – but one that works, until we have in MongoDb's aggregation pipeline a proper $utcOffset function.