code: def isRecord(self, db=None):
          
          if db is not None:
              same_db = db == self.context().db
  
          if db is None or same_db:
              col = self.schema().idColumn()
              with ReadLocker(self.__dataLock):
                  return (col in self.__loaded) and (self.__values[col.name()][0] is not None)
          else:
              return None
docs: Returns whether or not this database table record exists
          in the database.
  
          :return     <bool>