[jira] [Updated] (KAFKA-3430) Allow users to set key in KTable.toStream() and KStream

["Guozhang Wang (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-3430?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Guozhang Wang updated KAFKA-3430:
---------------------------------
    Component/s: kafka streams

> Allow users to set key in KTable.toStream() and KStream
> -------------------------------------------------------
>
>                 Key: KAFKA-3430
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3430
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: kafka streams
>            Reporter: Guozhang Wang
>             Fix For: 0.10.0.1
>
>
> Currently KTable.toStream does not take any parameters and hence users who wants to set the key need to do two steps:
> {code}table.toStream().map(...){code} in order to do so. We can make it in one step by providing the mapper parameter in toStream.
> And similarly today users usually need to call {code} KStream.map() {code} in order to select the key before aggregation-by-key operation if the original stream is does not contain keys. 
> We can consider adding a specific function in KStream to do so:
> {code}KStream.selectKey(mapper){code}
> which essential is the same as
> {code}KStream.map(/* mapper that does not change the value, but only the key */){code}



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