code: def prefetch_primary_key?(table_name = nil)
        return true if table_name.nil?
        table_name = table_name.to_s
        primary_keys(table_name.to_s).size == 0
      end
docs: If true, next_sequence_value is called before each insert statement
   to set the record's primary key.
   By default DB2 for i supports IDENTITY_VAL_LOCAL for tables that have
   one primary key.