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https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16442954#comment-16442954
]
ASF GitHub Bot commented on AVRO-1340:
--------------------------------------
BirdHowl commented on issue #298: AVRO-1340: Added Enum Defaults and unit tests.
URL: https://github.com/apache/avro/pull/298#issuecomment-382476911
> We could add an `@default` annotation now, or commit this now and add
that later, I don't have a strong feeling.
I think there's some misunderstanding here - `@default` already works, since
IDL lets _any_ JSON property be set through annotations (although that behavior
isn't well-documented). Anything that doesn't work as an annotation doesn't
work because of being a reserved property. `default`, however is a reserved
property only for fields.
If I take this a protocol file named `test.avdl`:
```
protocol Test {
@default("UNKNOWN")
enum Status {
SUCCESS,
FAILURE,
UNKNOWN
}
}
```
And then run `avro-tools.jar idl test.avdl` (tested on both this branch and
`master`), I get this output:
```
{
"protocol" : "Test",
"namespace" : null,
"types" : [ {
"type" : "enum",
"name" : "Status",
"symbols" : [ "SUCCESS", "FAILURE", "UNKNOWN" ],
"default" : "UNKNOWN"
} ],
"messages" : { }
}
```
In my JIRA post, I was attempting to provide reasonable answers to the
question: "how should we handle cases when both `@default` and the new `=`
syntax are present."
(Currently on this branch, if I use both I get JSON like:
```
{
"protocol" : "Test",
"namespace" : null,
"types" : [ {
"type" : "enum",
"name" : "Status",
"symbols" : [ "SUCCESS", "FAILURE", "UNKNOWN" ],
"default" : "FAILURE",
"default" : "UNKOWN"
} ],
"messages" : { }
}
```
)
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> 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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