Is there a way to access a Date as milliseconds since epoch (Date.getTime()) in mongodb aggregation pipeline

Question

Mongodb provides lots of 'Date Aggregation Operators' such as $dayOfYear, $dayOf Month, and $millisecond. The $millisecond function just returns the milliseconds of the time stamp with a range of 0-999.

Is there a way to access a Date object as milliseconds since epoch in aggregation pipeline?

Thanks,

Nathan

Directoire

Answer 1

You can $subtract the epoch date and the result will be your date milliseconds since epoch:

db.collection.aggregate([
    {$project : {
        "dateInMillis" : {$subtract : ["$date", new Date("1-1-1970")] }
    }}
]);

Mccusker

Thanks for the quick turn around. Seems like an odd way of getting the value but it works – Directoire

@NathanReese It's not odd at all once you realize that the underlying BSON date is actually an epoch timestamp. Which is all this does. The difference between now and the beginning in milliseconds. en.wikipedia.org/wiki/Unix_time – Meir

Make sure to parse date as UTC 'new Date(Date.UTC('1-1-1970'))' – Directoire

new Date(0) should also give you the 'beginning of time' epoch – Indulge

@AchintyaAshok and new Date(0) also ensures that local/server time zone doesn't cause any issues – Heartstrings

Answer 2

Here's how you can add an aggregation pipeline.

Oakland