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https://issues.apache.org/jira/browse/PIG-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875242#action_12875242
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Aniket Mokashi commented on PIG-972:
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Approach-
1. To implement above mentioned functionality, parser keeps track of all the
nested aliases it comes across and adds them to LOForEach.
2. After we parse the query (foreach), we dump the schema for all
nested-aliases stored in the list.
3. When describe foreach-alias; is queried, along with schema for
foreach-alias, we dump the schema for all nested-aliases stored in the list.
Data Structures -
Adding mDescribedAliasList to LOForEach to list all the "described" nested
aliases.
LOForeach has mForEachPlans which creates plan for all projections. This keeps
track of schemas for all nested aliases inside leaves of its plans.
Issues-
Verification of aliases in nested describe- As, we do not create a map for
nested aliases, it is not possible to validate upfront the name of the alias
used in nested describe.
Multiple dumps- Above approach might lead to multiple dumping of schemas.
These issues can be solved with adding more state into LOForeach.
> Make describe work with nested foreach
> --------------------------------------
>
> Key: PIG-972
> URL: https://issues.apache.org/jira/browse/PIG-972
> Project: Pig
> Issue Type: Improvement
> Reporter: Olga Natkovich
> Assignee: Aniket Mokashi
> Fix For: 0.8.0
>
>
> Currently Parser can't deal with that. This is because describe is part of
> Grunt parser while the rest of nested foreach is handled by the QueryParser
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