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https://issues.apache.org/jira/browse/AVRO-2772?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17748099#comment-17748099
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Christophe Le Saec commented on AVRO-2772:
------------------------------------------
Hello
If the output schema is compatible with input schema, then input record will be
simply copied to output record, whatever the name of two record schemas.
In your example, changing the name of record B from amount to amount1 will
generate an error as "Found B, expecting union".
That's why i think there is no error here.
> wrong union schema forward compatibility
> -----------------------------------------
>
> Key: AVRO-2772
> URL: https://issues.apache.org/jira/browse/AVRO-2772
> Project: Apache Avro
> Issue Type: Bug
> Components: java
> Affects Versions: 1.9.2
> Environment: JDK 13, Maven 3.6.3, avro 1.9.2.
> Reporter: Yubao Liu
> Priority: Major
> Attachments: avro-union.tar.gz
>
>
> {code:java}
> protocol Test {
> record A {
> int amount;
> }
> record B {
> int amount;
> }
> record C {
> // old:
> union { A } c;
>
> // new:
> union { A, B} c;
> }
> }
> {code}
> The old C schema has "union \{A} c;", new C schema has "union \{A, B} c;",
> suppose we use new C schema and write a B object for field "c", and use
> old C schema to read it back, AVRO will happily return a "A" object for
> field "c", this is surprising.
> The new and old schema are mutual compatible according to AVRO schema
> validator.
> Attached a maven project to demonstrate the issue, here is the output:
> {code}
> readerSchema and writerSchema are mutual compatible
> writerSchema unionSchemas.size()=2
> writerSchema
> unionSchemas.get(1)={"type":"record","name":"B","fields":[{"name":"amount","type":"int"}]}
> r={"c": {"amount": 12}}
> r.c.schema={"type":"record","name":"B","fields":[{"name":"amount","type":"int"}]}
> r2={"c": {"amount": 12}}
> r2.c.schema={"type":"record","name":"A","fields":[{"name":"amount","type":"int"}]}
> {code}
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