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https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16459837#comment-16459837
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ASF GitHub Bot commented on AVRO-1340:
--------------------------------------
cutting commented on a change in pull request #298: AVRO-1340: Added Enum
Defaults and unit tests.
URL: https://github.com/apache/avro/pull/298#discussion_r185267660
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File path: doc/src/content/xdocs/idl.xml
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@@ -152,14 +152,24 @@ protocol MyProtocol {
<section id="format_enums">
<title>Defining an Enumeration</title>
<p>
- Enums are defined in Avro IDL using a syntax similar to C or Java:
+ Enums are defined in Avro IDL using a syntax similar to C or Java.
They may also be defined with an optional default.
+ In the case that a reader schema is unable to recognize a symbol
written by the writer, the reader will fall back to using the defined default
value.
+ Note that this default is only used when an incompatible symbol is
read but not if the enum field is missing.
+ Example Writer Schema:
</p>
<source>
-enum Suit {
- SPADES, DIAMONDS, CLUBS, HEARTS
-}
+ enum Shapes {
+ SQUARE, TRIANGLE, CIRCLE, OVAL
+ }
+ </source>
+ <p>Example Reader Schema</p>
+ <source>
+ enum Shapes {
+ SQUARE, TRIANGLE, CIRCLE
+ } = CIRCLE
Review comment:
This needs a semicolon. I don't know if that's the best syntax, but it is
what we implemented!
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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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