danielcweeks commented on code in PR #16777: URL: https://github.com/apache/iceberg/pull/16777#discussion_r4495645243
########## format/spec.md: ########## @@ -372,6 +373,14 @@ The `initial-default` is set only when a field is added to an existing schema. T The `initial-default` and `write-default` produce SQL default value behavior, without rewriting data files. SQL default value behavior when a field is added handles all existing rows as though the rows were written with the new field's default value. Default value changes may only affect future records and all known fields are written into data files. Omitting a known field when writing a data file is never allowed. The write default for a field must be written if a field is not supplied to a write. If the write default for a required field is not set, the writer must fail. +In v4, a field's `write-default` may be a [value expression](expressions-spec.md). This allows defaults such as `current_timestamp()` to be evaluated when a row is written. A value expression `write-default` is subject to the following requirements: + +* The expression must be a constant or a function application (apply); [field references](expressions-spec.md#field-reference) are not allowed in a default value expression +* The expression must produce a value of the field's type, subject to [type promotion](#schema-evolution) Review Comment: I don't think we need to clarify this in the spec as it's an implementation issue. The main concern is that the resulting value from the expression needs to be written in compliance with the write schema. The implementation is responsible for ensuring that happens. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
