Ayoub Omari created KAFKA-16434:
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Summary: ForeignKey INNER join does not unset join result when FK
becomes null
Key: KAFKA-16434
URL: https://issues.apache.org/jira/browse/KAFKA-16434
Project: Kafka
Issue Type: Bug
Components: streams
Affects Versions: 3.7.0, 2.8.2
Reporter: Ayoub Omari
We have two topics : _left-topic[String, LeftRecord]_ and _right-topic[String,
String]_
where _LeftRecord_ :
{code:scala}
case class LeftRecord(foreignKey: String, name: String){code}
we do a simple *INNER* foreign key join on left-topic's foreignKey field. The
resulting join value is the value in right-topic. (same topology example as in
KAFKA-16407)
*Scenario: Unset foreign key of a primary key*
{code:scala}
rightTopic.pipeInput("fk1", "1")
leftTopic.pipeInput("pk1", ProductValue("fk1", "pk1"))
leftTopic.pipeInput("pk1", ProductValue(null, "pk1"))
{code}
*+Actual result+*
{code:java}
KeyValue(pk1, 3) {code}
*+Expected result+*
{code:java}
KeyValue(pk1, 3)
KeyValue(pk1, null) // This unsets the join between pk1 and fk1{code}
However, in {+}other cases{+}, where the join result should be unset (e.g. the
primary key is deleted, or the foreign key changes to a non existing FK), that
record is {+}correctly emitted{+}.
Also, the importance of unsetting the join result is mentioned in the code:
https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/kstream/internals/foreignkeyjoin/SubscriptionSendProcessorSupplier.java#L161C21-L163C36
{code:java}
//[...] Additionally, propagate null if no FK is found there,
// since we must "unset" any output set by the previous FK-join. This is true
for both INNER and LEFT join. {code}
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