code: def migrate(self):
          
          with io.open(self.json_file, 'rt', encoding='utf8') as fh:
              threads = json.load(fh)
          progress = Progress(len(threads))
  
          for i, thread in enumerate(threads):
              progress.update(i, str(i))
              self.insert(thread)
  
          progress.finish("{0} threads, {1} comments".format(len(threads), self.count))
docs: Process the input file and fill the DB.