[jira] [Commented] (KAFKA-4217) KStream.transform equivalent of flatMap

["Bruno Cadonna (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-4217?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16472499#comment-16472499 ] 

Bruno Cadonna commented on KAFKA-4217:
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Is this issue still relevant? The docs of [{{transform}}|https://kafka.apache.org/11/javadoc/org/apache/kafka/streams/kstream/KStream.html#transform-org.apache.kafka.streams.kstream.TransformerSupplier-java.lang.String...-] say "Transform each record of the input stream into zero or more records in the output stream", which sounds to me as if this issue has been already resolved.

> KStream.transform equivalent of flatMap
> ---------------------------------------
>
>                 Key: KAFKA-4217
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4217
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 0.10.0.1
>            Reporter: Elias Levy
>            Priority: Major
>              Labels: api, needs-kip, newbie
>
> {{KStream.transform}} gives you access to state stores while allowing you to return zero or one transformed {{KeyValue}}.  Alas, it is unclear what method you should use if you want to access state stores and return zero or multiple {{KeyValue}}.  Presumably you can use {{transform}}, always return {{null}}, and use {{ProcessorContext.forward}} to emit {{KeyValues}}.
> It may be good to introduce a {{transform}}-like {{flatMap}} equivalent, or allow store access from other {{KStream}} methods, such as {{flatMap}} itself.



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