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https://issues.apache.org/jira/browse/FLINK-17074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17079489#comment-17079489
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Timo Walther commented on FLINK-17074:
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Big +1 on this. It would also simplify the `CompositeType` subclasses quite a
lot.
> Deprecate DataStream.keyBy() that use tuple/expression keys
> -----------------------------------------------------------
>
> Key: FLINK-17074
> URL: https://issues.apache.org/jira/browse/FLINK-17074
> Project: Flink
> Issue Type: Improvement
> Components: API / DataStream
> Environment: Currently you can either specify a {{KeySelector}},
> tuple positions, and expression keys? I think {{KeySelectors}} are strictly
> superior and with lambdas (or function references) quite easy to use.
> Tuple/expression keys use reflection underneath to do the field accesses, so
> performance is strictly worse. Also, when using a {{KeySelector}} you will
> have a meaningful key type {{KEY}} in your operations while for
> tuple/expression keys the key type is simply {{Tuple}}.
> Tuple/expression keys were introduced before Java got support for lambdas in
> Java 8 and before we added the Table API. Nowadays, using a lambda is little
> more typing than using an expression key but is (possibly) faster and more
> type safe. The Table API should be used for these more
> expression-based/relational use cases.
> Reporter: Aljoscha Krettek
> Priority: Major
> Labels: starter
> Fix For: 1.11.0
>
>
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