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

["Suresh TL (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16888251#comment-16888251 ] 

Suresh TL commented on AVRO-1340:
---------------------------------

I see from the unit tests for testing enum default value, that the writer schema is still needed for the reader to understand / decode the data.

[https://github.com/apache/avro/blob/master/lang/java/avro/src/test/java/org/apache/avro/TestSchemaCompatibilityEnumDefaults.java#L122]

Is it possible for the reader to use enum default values, when data is sent without schema ? 

For eg: 

Reader schema can have enum with  \{ "A" , "B" } and enum default "A"

Writer schema can have enum with \{ "A", "B" , "C", "D" , "E" } and enum default "A" 

And value being sent is say "E"

 

 

> use default to allow old readers to specify default enum value when encountering new enum symbols
> -------------------------------------------------------------------------------------------------
>
>                 Key: AVRO-1340
>                 URL: https://issues.apache.org/jira/browse/AVRO-1340
>             Project: Apache Avro
>          Issue Type: Improvement
>          Components: spec
>         Environment: N/A
>            Reporter: Jim Donofrio
>            Assignee: Adam Bellemare
>            Priority: Minor
>             Fix For: 1.9.0
>
>
> 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.



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