[AVRO-1340] use default to allow old readers to specify default enum value when encountering new enum symbols

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.9.0
• Component/s: spec

Environment

N/A

• Hadoop Flags: Incompatible change
• Assignee: Adam Bellemare
• Reporter: Jim Donofrio
• Created: 25/May/13 05:35
• Updated: 23/May/23 14:18
• Resolved: 02/May/18 16:57

Description

The schema resolution page says:

> if both are enums:
> if the writer's symbol is not present in the reader's enum, then an
error is signalled.

This makes it difficult to use enum's because you can never add a enum value and keep old reader's compatible. Why not use the default option to refer to one of enum values so that when a old reader encounters a enum ordinal it does not recognize, it can default to the optional schema provided one. If the old schema does not provide a default then the older reader can continue to fail as it does today.

Issue Links

• causes: AVRO-2767 Can't easily use Java annotations to set enum default
• is related to: AVRO-1347 Improve name and alias matching for named schemas
• relates to: AVRO-3760 Using enum with default symbol, cannot parse future value
• relates to: AVRO-2626 [enums] avro-js does not seem to support 1.9.0 spec although 1.9.0 version was published
• relates to: AVRO-1752 Aliases for enum symbols.
• relates to: AVRO-2895 Use default to allow old readers to specify default union value when encountering new union branches
• Testing discovered: AVRO-3313 enum default value to allow deserializer to deserialize to when encountering new enum symbols doesn't work
• links to: GitHub Pull Request #163
• links to: GitHub Pull Request #163
• links to: GitHub Pull Request #298
• links to: GitHub Pull Request #357