[jira] [Created] (AVRO-2772) wrong union schema forward compatibility

["Yubao Liu (Jira)" <ji...@apache.org>]

Yubao Liu created AVRO-2772:
-------------------------------

             Summary: 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
         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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