Extract object creation timestamps from Mongo object IDs and create Mongo ID with certain timestamps to query date ranges

mongoIDsAndDatesUtils.js

// Cretes a Mongo ID form a timestamp
// Useful when we want to query a collection on date ranges
function idWithTimestamp(timestamp) {
	
	// Convert string or unix time date to Date object (otherwise assume timestamp is a date)
	if ( typeof(timestamp) == 'string' || typeof(timestamp) == 'number' ) {
		timestamp = new Date(timestamp);
	}

	// Convert date object to hex seconds since Unix epoch
	var hexSeconds = Math.floor(timestamp/1000).toString(16);

	// Create an ObjectId with that hex timestamp
	var constructedObjectId = ObjectId(hexSeconds + "0000000000000000");

	return constructedObjectId
}


// Extracts the timestamp an object was created at 
// from the auto-generated Mongo ID
function extractTimestampFrom(id) { 
	
	return new Date( parseInt( id.toString().substring(0,8), 16 ) * 1000 );
	
}


// Extracts all the objects within a particular dates range in a collection
// that are also in a certain channel
db.log.find({ _id: { $gt: idWithTimestamp(1422473700000), $lt: idWithTimestamp(1422477900000) }, "channel":"roomquake/new_observation" });