Convert document field type in MongoDB.

gistfile1.js

// list of $type values: http://docs.mongodb.org/manual/reference/operator/type/
db.person.find( { 'integer_id' : { $type : 2 } } ).forEach( function (x) {   
  x.integer_id = new NumberLong(x.integer_id); // convert field to Long
  db.person.save(x);
});