new_contents: ''' imports from installed packages '''
  from django.core.management.base import BaseCommand, CommandError
  
  from django_mongokit import get_database
  
  try:
      from bson import ObjectId
  except ImportError:  # old pymongo
      from pymongo.objectid import ObjectId
  
  ''' imports from application folders/files '''
  from gnowsys_ndf.ndf.models import Node, Triple, HistoryManager
  from gnowsys_ndf.ndf.rcslib import RCS
  
  ####################################################################################################################
  
  class Command(BaseCommand):
      """This update-script updates attribute_type field's value (of all GAttribute instances) from ObjectId to it's corresponding DBRef; and also creates it's version-file(history) in rcs-repo.
      """
  
      help = "\tThis update-script updates attribute_type field's value (of all GAttribute instances) from ObjectId to it's corresponding DBRef; and also creates it's version-file(history) in rcs-repo."
  
      def handle(self, *args, **options):
  
          history_manager = HistoryManager()
          rcs_obj = RCS()
  
          collection = get_database()[Triple.collection_name]
          cur = collection.Triple.find( {'_type': 'GAttribute'} )
          
          for n in cur:
              if type(n.attribute_type) == ObjectId:
                  # Retrieving attribute-type document(or object) from it's ObjectId stored in GAttribute's attribute_type field 
                  attr_type = collection.Node.one( {'_id': n.attribute_type} )
  
                  # Replacing GAttribute's attribute_type field value from ObjectId to DBRef
                  n.attribute_type = attr_type
  
                  subject_doc = collection.Node.one({'_id': n.subject})
  
                  n.name = subject_doc.name + " -- " + n.attribute_type['name'] + " -- " + n.object_value
  
                  if history_manager.create_or_replace_json_file(n):
                      fp = history_manager.get_file_path(n)
                      message = "This document (" + n.name + ") is created on " + subject_doc.created_at.strftime("%d %B %Y")
                      rcs_obj.checkin(fp, 1, message.encode('utf-8'), "-i")
  
                  n.save()
  
          # --- End of handle() ---
  
  
subject: Update script for updating attribute_type field of GAttribute instances from ObjectId to DBRef (AttributeType)