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From "Guozhang Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4217) KStream.transform equivalent of flatMap
Date Fri, 01 Sep 2017 03:11:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4217?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16149971#comment-16149971
] 

Guozhang Wang commented on KAFKA-4217:
--------------------------------------

{{valueTransformerSupplier}} will return a {{ValueTransformer}} that has a {{transform}} function,
and it has similar functionality as {{valueMapper}}.

> 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
>              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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