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https://issues.apache.org/jira/browse/AVRO-2918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17569480#comment-17569480
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Christophe Le Saec commented on AVRO-2918:
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As a possible example of polymorphism, i built this [Pull
Request|https://github.com/apache/avro/pull/1776].
This use a discriminator when a value is a subtype of declaration (if a field
is declared as Person and its real value is Employee for example, or in an
array of Person, each Employee instance will use a discriminator).
- For schema set, sub schemas will be stored in Names during parsing
(parse(JsonNode schema, Names names)).
Otherwise, Protocol class does the Job ({_}this is a pb i already faced when
building a PR for AVRO-530, allowing using schema before it is define, and so,
allowing mutual recursion{_}).
- Encoding / decoding are taken into account(need to add more tests)
- I didn't test generated code.
(_Code is inspired of what was already done with Union_)
> 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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