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https://issues.apache.org/jira/browse/KAFKA-7653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16699383#comment-16699383
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John Roesler commented on KAFKA-7653:
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Hi [~mark.tranter],
I haven't looked at the PR yet, but just one comment from the discussion here...
It's a sharp edge, but AFAIK users *must* provide different serde instances for
keys/values. I recently submitted a bugfix for the scala API to make the
provided implicit serdes generate a new instance each time, as this was
overlooked initially.
I'm wondering if, in addition to what you proposed above, we should consider
verifying that the serdes are properly configured, possibly in the Scala API,
but possibly more usefully in the Java API.
Thoughts?
> Streams-Scala: Add type level differentiation for Key and Value serdes.
> -----------------------------------------------------------------------
>
> Key: KAFKA-7653
> URL: https://issues.apache.org/jira/browse/KAFKA-7653
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Mark Tranter
> Assignee: Mark Tranter
> Priority: Minor
> Labels: scala
>
> Implicit resolution/conversion of Serdes/Consumed etc is a big improvement
> for the Scala Streams API. However in cases where a user needs to
> differentiate between Key and Value serializer functionality (i.e. using the
> Schema Registry), implicit resolution doesn't help and could cause issues.
> e.g.
> {code:java}
> case class MouseClickEvent(pageId: Long, userId: String)
> builder
> // Long serde taken from implicit scope configured with
> // `isKey` = true
> .stream[Long, MouseClickEvent]("mouse-clicks")
> .selectKey((_,v) => v.userId)
> .groupByKey
> .aggregate(() => 0L, (_: String, mce: MouseClickEvent, count: Long) =>
> count + 1)
> .toStream
> // Same Long serde taken from implicit scope configured with
> // `isKey` = true, even thought the `Long` value in this case
> // will be the Value
> .to("mouse-clicks-by-user")
> {code}
> It would be ideal if Key and Value Serde/SerdeWrapper types/type classes
> could be introduced to overcome this limitation.
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