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From "Fabian Hueske (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-925) Support KeySelector function returning Tuples
Date Sat, 28 Jun 2014 21:23:24 GMT

    [ https://issues.apache.org/jira/browse/FLINK-925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14046967#comment-14046967

Fabian Hueske commented on FLINK-925:

I am pretty sure that CoGroup uses the same mechanism as GroupBy (reduce) and Join. The missing
restriction for Comparable return types of the KeySelector was just missing.

The limitation that a grouping key may only be an atomic type must be relaxed for this issue
such that also Tuples that contain atomic types are supported. 
So in order to solve this issue you need to add support for having a Tuple with atomic types
as a key.

> Support KeySelector function returning Tuples
> ---------------------------------------------
>                 Key: FLINK-925
>                 URL: https://issues.apache.org/jira/browse/FLINK-925
>             Project: Flink
>          Issue Type: Improvement
>    Affects Versions: 0.6-incubating
>            Reporter: Fabian Hueske
>            Assignee: Tobias
>            Priority: Minor
>              Labels: starter
> KeySelector functions are used to extract keys on which DataSets can be grouped or joined.
> Currently, the keys types returned by KeySelector function are restricted to be comparable.
However, Flinks Tuple data types are not comparable (because this depends on the types of
its fields) which makes grouping and joining on composite keys difficult.
> We should change the signature of the groupBy(), join(), and coGroup() methods to allow
also non-comparable keys as return types of a KeySelector function. 
> Instead we will check at optimization time whether the returned type is comparable (which
is true for tuples if all elements are comparable).

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