code: def _prepareOldVersionOf(self, typename, version, persistedSchema):
          
          appropriateSchema = persistedSchema[typename, version]
          # create actual attribute objects
          dummyAttributes = {}
          for (attribute, sqlType, indexed, pythontype,
               docstring) in appropriateSchema:
              atr = pythontype(indexed=indexed, doc=docstring)
              dummyAttributes[attribute] = atr
          dummyBases = []
          oldType = declareLegacyItem(
              typename, version, dummyAttributes, dummyBases)
          self._upgradeManager.queueTypeUpgrade(oldType)
          return oldType
docs: Note that this database contains old versions of a particular type.
          Create the appropriate dummy item subclass and queue the type to be
          upgraded.
  
          @param typename: The I{typeName} associated with the schema for which
              to create a dummy item class.
  
          @param version: The I{schemaVersion} of the old version of the schema
              for which to create a dummy item class.
  
          @param persistedSchema: A mapping giving information about all schemas
              stored in the database, used to create the attributes of the dummy
              item class.