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Posted to issues@beam.apache.org by "Yueyang Qiu (JIRA)" <ji...@apache.org> on 2019/05/14 23:57:00 UTC

[jira] [Commented] (BEAM-7301) Beam transforms reorder fields

    [ https://issues.apache.org/jira/browse/BEAM-7301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16839875#comment-16839875 ] 

Yueyang Qiu commented on BEAM-7301:
-----------------------------------

Context: [https://github.com/apache/beam/pull/8425]

> Beam transforms reorder fields
> ------------------------------
>
>                 Key: BEAM-7301
>                 URL: https://issues.apache.org/jira/browse/BEAM-7301
>             Project: Beam
>          Issue Type: Sub-task
>          Components: sdk-java-core
>            Reporter: Reuven Lax
>            Assignee: Yueyang Qiu
>            Priority: Major
>
> Currently transforms such as Select, DropFields, RenameFields, and AddFields can create schemas with unexpected order. The problem is that FieldAccessDescriptor stores top-level fields and nested fields separately, so there's no way to tell the relative order between them. To fix this we should refactor FieldAccessDescriptor: instead of storing these separately it should store a single list, where each item in the list might optionally have a nested FieldAccessDescriptor.
> Expected behavior from the transforms:
>    DropFields: preserves order in original schema
>    RenameFields: preserves order in original schema
>    AddFields: adds fields in order specified. If multiple nested fields are selected, the first reference to the top field wins (e.g. adding "a.b", "c", "a.d" results in adding a before c.
>   Select: Select fields in the order specified.



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