code: public List<K> getSavedIds() {
          if (dbObjects.length > 0 && dbObjects[0] instanceof JacksonDBObject) {
              throw new UnsupportedOperationException("Generated _id retrieval not supported when using stream serialization");
          }
  
          List<K> ids = new ArrayList<K>();
          for (int i = 0; i < dbObjects.length; i++) {
              ids.add((K) jacksonDBCollection.convertFromDbId(dbObjects[i].get("_id")));
          }
  
          return ids;
      }
docs: Get the saved IDs.  This may be useful for finding out the IDs that were generated by MongoDB if no IDs were
  supplied.
  
  @return The saved IDs