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https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16331615#comment-16331615
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Adam Bellemare commented on AVRO-1340:
--------------------------------------
The "None" column was meant to indicate that there was no field with that name
present. I have updated the doc to change "None" to "No Field Present". This
means the field did not exist in the writers schema.
I think we are largely in agreement. The only point of contention I have is
that in scenario 2 you listed above, using the field-default for an unknown
symbol changes the existing functionality. Instead of an exception being
thrown, the default value will be assigned.
{code:java}
"fields" : [ {
"name" : "foo",
"type" : {
"type" : "enum",
"name" : "Bar",
"symbols" : [ "A", "B", "FieldDefault"]
},
"default" : "FieldDefault"
}]
{code}
If the schema above is used currently and a Writer writes with Symbol "C", upon
reading the schema the Reader will throw an "Error reading Avro:
org.apache.avro.AvroTypeException: No match for C". With the change you
propose, it would not throw an exception but instead return "FieldDefault",
though the schema would be the same in both cases. Do I understand that
scenario correctly? My only real concern is about breaking existing behaviour.
> 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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