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https://issues.apache.org/jira/browse/FLINK-925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14050058#comment-14050058
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Tobias commented on FLINK-925:
------------------------------
I added a case so that tuples in tuples are compared using all their keys. So
when a Tuple is key field, a TupleComparator is created, which is using *all
fields as key*.
[https://github.com/tobwiens/incubator-flink/commit/bd086ed9d1cbca30fe8540fb08a3124926ed3305]
Therefore all nested tuples should work, even more than 2. Those are now broken
down until an atomic type or not supported (Exception thrown) type is reached.
I did not see any test cases for TupleTypeInfo.java.
Should I add test cases? And how would a good designed test case look like?
Since it has many possible execution paths and theoretically there could be
many tuples nested.
> 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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