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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3702) DataStream API PojoFieldAccessor doesn't support nested POJOs
Date Wed, 14 Sep 2016 11:10:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15490154#comment-15490154

ASF GitHub Bot commented on FLINK-3702:

Github user mbalassi commented on the issue:

    We have gone through the changes with @ggevay and found that the documentation is lacking
or misleading in a couple of cases.
    1. The DataStream API JavaDocs mention that one can aggregate on expressions including
Java Bean-like getters which is not true regardless of this change. [1]
    2. I think this is due to the confusion between the `KeySelectors` produced by the `Keys.ExpressionKeys`
and the String expressions that we can pass to an aggregation operator. E.g. one of the distinctions
between the two options are that the former can return a `CompositeType`, while we forbid
that to happen in the case of the latter as that could cause the aggregation itself to fail.
    3. The batch API aggregations do not have the overloaded version where you could pass
a field accessor string. Of course this is just a convenience method anyway, which is easily
implemented on the user side, e.g. as it is done in the `WordCountPojo` example. [2]
    As for this pull request I suggest to update the false Javadoc from the streaming API
and document in the concepts that the aggregation field accessors and the keyselectors are
slightly different due to there semantics.
    Other than this observation I like the changes and would like to have them in by the end
of next week.
    [1] https://github.com/apache/flink/blob/b8299bf92d8e3dbe140dd89602699394019b783d/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/KeyedStream.java#L295-L310
    [2] https://github.com/apache/flink/blob/b8299bf92d8e3dbe140dd89602699394019b783d/flink-examples/flink-examples-batch/src/main/java/org/apache/flink/examples/java/wordcount/WordCountPojo.java#L106-L111

> DataStream API PojoFieldAccessor doesn't support nested POJOs
> -------------------------------------------------------------
>                 Key: FLINK-3702
>                 URL: https://issues.apache.org/jira/browse/FLINK-3702
>             Project: Flink
>          Issue Type: Improvement
>          Components: DataStream API
>    Affects Versions: 1.0.0
>            Reporter: Robert Metzger
>            Assignee: Gabor Gevay
> The {{PojoFieldAccessor}} (which is used by {{.sum(String)}} and similar methods) doesn't
support nested POJOs right now.
> As part of FLINK-3697 I'll add a check for a nested POJO and fail with an exception.

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