[jira] [Assigned] (KAFKA-7653) Streams-Scala: Add type level differentiation for Key and Value serdes.

["Matthias J. Sax (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-7653?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax reassigned KAFKA-7653:
--------------------------------------

    Assignee:     (was: Mark Tranter)

> 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
>            Priority: Minor
>              Labels: kip, 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.
> KIP-513: [https://cwiki.apache.org/confluence/display/KAFKA/KIP-513%3A+Distinguish+between+Key+and+Value+serdes+in+scala+wrapper+library+for+kafka+streams]



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