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

["Mark Tranter (JIRA)" <ji...@apache.org>]

Mark Tranter created KAFKA-7653:
-----------------------------------

             Summary: 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


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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