Create MongoDB ObjectID from date in the past using PHP driver

Question

I have to import a lot of data into MongoDB from MySQL and I'd like to use the timestamp from the ObjectID instead of storing it in a separate key/value (as it is in the existing data). In order to do this I'd need to create an ObjectID for the existing data with a date from the past. I also need to do this using the PHP driver. I've read that there might be a way to do this in Python, Java and Node.JS so I thought maybe there was an equivalent method in PHP.

If this is possible - is it safe to do? Meaning and I going to have issues with duplicate or invalid ObjectIDs? Thanks.

In Node.JS:

var timestamp = Math.floor(new Date().getTime()/1000);
var objectId = new ObjectID(timestamp);

Below is from: MongoDB using timestamps to sort

In Python:

gen_time = datetime.datetime(2010, 1, 1)
dummy_id = ObjectId.from_datetime(gen_time)

In Java:

Date d = new Date(some timestamp in ms);
ObjectId id = new ObjectId(d)

Answer 1

Right now, the PHP driver has no built in functionality for this, the __set_state() that the other answer mentioned is only for being able to session-deserialize the ID and doesn't allow you to create it through the specific components.

You will have to do the following to automatically create an ID:

<?php
function createId( $yourTimestamp )
{
    static $inc = 0;

    $ts = pack( 'N', $yourTimestamp );
    $m = substr( md5( gethostname()), 0, 3 );
    $pid = pack( 'n', posix_getpid() );
    $trail = substr( pack( 'N', $inc++ ), 1, 3);

    $bin = sprintf("%s%s%s%s", $ts, $m, $pid, $trail);

    $id = '';
    for ($i = 0; $i < 12; $i++ )
    {
        $id .= sprintf("%02X", ord($bin[$i]));
    }
    return new MongoID($id);
}

var_dump( createId( time() ) );
?>

Answer 2

If you are using the MongoId just for comparison, for example, selecting all records within a date range, you don't need a fully valid id. So you could simply do:

$id = new \MongoId(dechex($timestamp) . str_repeat("0", 16));

Just be sure to never insert this id and just use it for $gte/$gt/$lt/$lte queries.

edit

My bad, the above snippet would work with dates before about 1979 as dechex($timestamp) doesn't always return 8 characters, so a better snippet would be:

$id = new \MongoId(sprintf("%08x%016x", $timestamp, 0));