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https://issues.apache.org/jira/browse/AVRO-2918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17569427#comment-17569427
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Jonathan Rapoport commented on AVRO-2918:
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I think the first option specified is the correct one to use. However somehow
this union of types should only contain subtypes of the base type. Perhaps a
union is not the option as it is cumbersome, but rather a marking that all
subtypes of a given type are accepted.
Notwithstanding, upcasting should still be an option to encode subclasses in an
array consisting solely of their parent type.
> Schema polymorphism
> -------------------
>
> Key: AVRO-2918
> URL: https://issues.apache.org/jira/browse/AVRO-2918
> Project: Apache Avro
> Issue Type: New Feature
> Components: logical types, misc, spec
> Reporter: Jonathan Rapoport
> Priority: Critical
> Labels: features
> Original Estimate: 96h
> Remaining Estimate: 96h
>
> Include the option to use named types as base types for a new schema. Allow
> for MRO generation. Field inheritance.
> The benefits of this approach include:
> * Defining a schema as validation for a certain wire, and so allowing the
> receiver to be certain of the structure of the data (this works today).
> However, defining an extension of this schema, or certain schemas which can
> be normalized to the original schema, but contain additional information,
> will not allow it to be sent over the same wire.
> * Backwards compatibility through inheritance - you never break the old
> schema, thus allowing a long integration period, with no need to recode all
> processes familiar with the schema. The new schema will simply inherit the
> old one, and only add information.
> * Allow for full data control through polymorphism, and the ability to
> replace structures within any supported language.
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