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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-1340) use default to allow old readers to specify default enum value when encountering new enum symbols
Date Tue, 05 Sep 2017 17:43:00 GMT

    [ https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16154041#comment-16154041
] 

Doug Cutting commented on AVRO-1340:
------------------------------------

I don't see how aliases alone resolve this issue.  If someone adds a new symbol and writes
new data containing it, what aliases would be used so that old code can read this new symbol?

Unless I'm missing something, aliases belong in a separate issue.  They don't enable addition
and deletion of symbols, but rather renamings.  A uniform mechanism that handled both might
be nice, but I don't see how aliases accomplish this, so until someone proposes such a mechanism,
let's keep the issues separate.

> 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: Avro
>          Issue Type: Improvement
>          Components: spec
>         Environment: N/A
>            Reporter: Jim Donofrio
>            Priority: Minor
>
> 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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