title: Mongodb c# driver - copy Id to another field on insert
body: <p>I'm using .Net - mongodb c# driver for monngodb. When inserting the document I want to copy generated <code>[BsonId] ObjectId Id</code> field to another field in the document (duplicating the value)</p>
  
  <p>I can run Insert, which will produce the key and then run update to copy the key to another field but this will leave the db in the "soft" state for a (brief) period of time.</p>
  
  <p>Is it possible to do this "atomically" or am I using mongodb wrong?</p>