title: Changing _id in MongoDb
body: <p>just curious - I've got a bunch of records in a MongoDB collection that have _id set to something that was defined outside Mongo (They are the ID's the data had when it was in MySQL, and the were imported with _id being set to the MySQL ID). What would be the best way (preferably with PHP) to convert those ID's to something Mongo generated?</p>
  
  <p>So instead of a record having _id = 500, it would have an _id = 53fcf8d6c4d3f7df129e3245.</p>
  
  <p>Thanks!</p>