Mongodb get the 3-byte counter from an ObjectId

Question

How/Can I get the

3-byte counter, starting with a random value

part from a mongodb ObjectId?

I have an ObjectId like this: ObjectId("507f1f77bcf86cd799439011")

According to mongodb documentation:

Description

ObjectId() Returns a new ObjectId value. The 12-byte ObjectId value consists of:

a 4-byte value representing the seconds since the Unix epoch,

a 3-byte machine identifier,

a 2-byte process id,

and a 3-byte counter, starting with a random value.

I want to get the "and a 3-byte counter, starting with a random value." part from the ObjectId above if its possible.

Solomon

can u elaborate your question please? – Huppah

Answer 1

You could try the following hack where you can get the equivalent string representation of the ObjectId using toString() or toHexString(), use parseInt and slice to get the parts. Because hex digits are half of a byte the offsets are twice as much:

db.collection("collectionName").findOne({}, function(err, result) {     
    if (result) {
        var id          = result._id.toString(), ctr = 0;
        var timestamp   = parseInt(id.slice(ctr, (ctr+=8)), 16);
        var machineID   = parseInt(id.slice(ctr, (ctr+=6)), 16);
        var processID   = parseInt(id.slice(ctr, (ctr+=4)), 16);
        var counter     = parseInt(id.slice(ctr, (ctr+=6)), 16);
        console.log(id);
        console.log(timestamp);
        console.log(machineID);
        console.log(processID);
        console.log(counter);                    
    }       
});

Scott

tested with "507f1f77bcf86cd799439011" here are the results: timestamp: 1350508407, machineId: 12384364, processID: 55193, counter: 4427793 These are all good but timestamp 1350508407 does not look ok. new Date(1350508407) = Fri Jan 16 1970 16:08:28 GMT+0100 (Romance Standard Time) – Solomon

Timestamp is not in milliseconds, you need to multiply by 1000 first to get the actual date i.e. new Date(1350508407*1000) = Wed Oct 17 2012 22:13:27 GMT+0100 (GMT Daylight Time) – Scott

on what basis the documents are sorted? I see all information identical for data inserted in bulk. – Bimbo

I'm using this for the counter and I'm seeing duplicate counters for different ID's. Is it supposed to be unique? – Plaided