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https://issues.apache.org/jira/browse/AVRO-1568?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14107552#comment-14107552
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Doug Cutting commented on AVRO-1568:
------------------------------------

bq. Maybe an API can be added to ReflectData as #addUnionSchema (Class 
baseClass, Class derivedClasses[])

I'd opt for something more general, like, #setSchema(Class,Schema).  We might 
then define a convenience method like #setUnionSchema(Class,Class...) in terms 
of that, but the underlying implementation would use a Map<Type,Schema>.

> Allow Java polymorphism in Avro for third-party code
> ----------------------------------------------------
>
>                 Key: AVRO-1568
>                 URL: https://issues.apache.org/jira/browse/AVRO-1568
>             Project: Avro
>          Issue Type: Improvement
>    Affects Versions: 1.7.6
>            Reporter: Sachin Goyal
>
> A large number of Java designs interacting with databases with 
> Hibernate/Couchbase (perhaps, even otherwise) have Java polymorphism of the 
> form:
> {code:java}
> class Base 
> {
>    Integer a = 5;
> }
> class Derived extends Base
> {
>     String b = "Foo";
> }
> class PolymorphicDO
> {
>    Base b = new Derived();
> }
> {code}
> Jackson handles this kind of field by using annotations such as:
> {code}
> @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = 
> JsonTypeInfo.As.PROPERTY, property = "@class”)
> {code}
> If such a thing can be added to Avro, all those Java designs could become 
> immediately usable with Avro. They would also become Hadoop compatible due to 
> AvroSerde.



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