[jira] [Commented] (FLINK-3538) DataStream join API does not enforce consistent usage

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3538?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15172118#comment-15172118 ] 

ASF GitHub Bot commented on FLINK-3538:
---------------------------------------

GitHub user aljoscha opened a pull request:

    https://github.com/apache/flink/pull/1740

    [FLINK-3538] Streamline Scala DataStream.join/coGroup

    This enforces that the user always has to specify keys for both inputs
    before .window() can be called.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/aljoscha/flink scala-stream-join-fix

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/1740.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #1740
    
----
commit 70391df2979ee59d6ddad96c8fcb0e6a5a74ebf1
Author: Aljoscha Krettek <al...@gmail.com>
Date:   2016-02-29T16:02:38Z

    [FLINK-3538] Streamline Scala DataStream.join/coGroup
    
    This enforces that the user always has to specify keys for both inputs
    before .window() can be called.

----


> DataStream join API does not enforce consistent usage
> -----------------------------------------------------
>
>                 Key: FLINK-3538
>                 URL: https://issues.apache.org/jira/browse/FLINK-3538
>             Project: Flink
>          Issue Type: Improvement
>          Components: DataStream API, Scala API
>    Affects Versions: 1.0.0
>            Reporter: Till Rohrmann
>            Assignee: Aljoscha Krettek
>
> In the Scala DataStream API the {{join}} operation does not enforce that the user has specified a {{KeySelector}} for both input sides before applying a window function. Moreover, the order of the {{where}} and {{equalTo}} clause is not fixed and it is possible to specify multiple {{where}} and {{equalTo}} clauses. In the latter case, it is not clear which {{KeySelector}} will eventually be used by the system.
> So the following Flink programs compile without a compilation problem (the first two lines will only fail at runtime):
> {code}
> inputA.join(inputB).equalTo{x => x}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
>       .apply(new DefaultFlatJoinFunction[String, String]()).print()
> inputA.join(inputB).where{x => x}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
>       .apply(new DefaultFlatJoinFunction[String, String]()).print()
> inputA.join(inputB).equalTo{x => x}.where{x => x}.where{x => "1"}.equalTo{x => "42"}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
>       .apply(new DefaultFlatJoinFunction[String, String]()).print()
> {code}
> This is unlike the Java DataStream API where a clear pattern of {{join}} then {{where}} and then {{equalTo}} is enforced. I would propose to do the same for the Scala API.



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