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