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https://issues.apache.org/jira/browse/KAFKA-7653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16701345#comment-16701345
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Guozhang Wang commented on KAFKA-7653:
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I think [~mark.tranter] is trying to provide a work-around if we cannot auto
configure the same serde class' instance with key turned on / off. If that is
possible, then I feel providing two instances of a single class of serde whose
which will be configured differently for key and value would be ideal; if this
cannot be achieved, then we need to consider using two classes, and passing in
the instance of each class respectively for key and value.
Note that https://issues.apache.org/jira/browse/KAFKA-3729 was filed before we
have KIP-182; now with key / value serdes wrapped in Produced / Consumed /
Grouped etc, we know exactly which serde is used for key / value, and hence
should be able to auto-configure them accordingly inside the constructor of
those control objects. Then with that this ticket should be easy to resolve,
does that make sense?
> 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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