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https://issues.apache.org/jira/browse/KAFKA-7653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16695446#comment-16695446
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Matthias J. Sax commented on KAFKA-7653:
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I want to share another thought about this (brought up by [~miguno] in a
discussion we had). The issue, that user-provided serdes on operators need to
be configure() manually by the user before they are handed into the operator,
also exists for the Java API. It's less problematic in Java because there are
no explicits.
However, IMHO there is actually not reason why Streams could not auto-config
all provided serdes (not just the default ones from the config). If we would do
this, this would implicitly fix this ticket (as it would apply to the shared
runtime) and we don't need any API change.
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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