code: public void ensureIndex(final DBObject keys, final DBObject optionsIN) throws MongoException {
          dbCollection.ensureIndex(keys, optionsIN);
      }
docs: Creates an index on a set of fields, if one does not already exist.
  
  @param keys      an object with a key set of the fields desired for the index
  @param optionsIN options for the index (name, unique, etc)
  @throws MongoException If an error occurred