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https://issues.apache.org/jira/browse/FLINK-2668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14745415#comment-14745415
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Aljoscha Krettek commented on FLINK-2668:
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IMHO it seems more intuitive that a second {{project}} call would project based
on the already projected fields and not add more fields to the already present
projected fields.
This would also make [~greghogan]'s case work.
> ProjectOperator method to close projection
> ------------------------------------------
>
> Key: FLINK-2668
> URL: https://issues.apache.org/jira/browse/FLINK-2668
> Project: Flink
> Issue Type: Improvement
> Components: Java API
> Affects Versions: master
> Reporter: Greg Hogan
> Priority: Minor
>
> I have come across an issue in my code where I called project(...) on a
> {{DataSet}} which was already a {{ProjectOperator}}. Instead of reducing the
> number of fields from 2 to 1 this instead increased the number of fields from
> 2 to 3 resulting in
> {{org.apache.flink.api.common.functions.InvalidTypesException: Input
> mismatch: Tuple arity '3' expected but was '1'.}} when processing the next
> operator.
> This can be resolved by adding an optional explicit call to conclude the
> projection, perhaps {{ProjectOperator.closeProjection()}}. Can this be done
> without creating a new no-op operator?
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