keySet property

key_set identifies the rows to be yielded.

key_set names the primary keys of the rows in table to be yielded, unless index is present. If index is present, then key_set instead names index keys in index. If the partition_token field is empty, rows are yielded in table primary key order (if index is empty) or index key order (if index is non-empty). If the partition_token field isn't empty, rows are yielded in an unspecified order. It isn't an error for the key_set to name rows that don't exist in the database. Read yields nothing for nonexistent rows.

Required.