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From "Andy Schlaikjer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PIG-2715) Cannot specify schema field alias for map value via piglatin
Date Tue, 22 May 2012 23:44:42 GMT

    [ https://issues.apache.org/jira/browse/PIG-2715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281319#comment-13281319
] 

Andy Schlaikjer commented on PIG-2715:
--------------------------------------

> When you print out the schema, there is no alias: "map[int]". And we will not parse "map[count:int]".

When I "DESCRIBE relation_with_map_with_value_alias" I *do* see map value alias e.g. "map[count:
int]" when code has programmatically set the alias, in this case within a LoadFunc implementation.
                
> Cannot specify schema field alias for map value via piglatin
> ------------------------------------------------------------
>
>                 Key: PIG-2715
>                 URL: https://issues.apache.org/jira/browse/PIG-2715
>             Project: Pig
>          Issue Type: Bug
>          Components: parser
>    Affects Versions: 0.10.0
>            Reporter: Andy Schlaikjer
>
> Programmatically, pig components are able to define schema field aliases for map values,
but the same cannot be done via piglatin. For example:
> {code}
> %default INPUT_PATH 'map_value_alias_bug.tsv';
> A = LOAD '$INPUT_PATH' AS (
>   id: long,
>   -- events: [count: int] -- parse failure
>   events: [int]
> );
> DESCRIBE A;
> A = FOREACH A GENERATE
>   id,
>   -- (map[count: int]) events -- parse failure
>   -- ([count: int]) events -- parse failure
>   -- events: [count: int] -- parse failure
>   -- events AS [count: int] -- parse failure
>   -- events AS events: [count: int] -- parse failure
>   ([int]) events -- this is okay
>   ;
> DESCRIBE A;
> quit;
> {code}
> When using the [Elephant Bird project|https://github.com/kevinweil/elephant-bird/]'s
[ThriftToPig utility|https://github.com/kevinweil/elephant-bird/blob/master/src/java/com/twitter/elephantbird/pig/util/ThriftToPig.java#L273]
along with a Thrift message spec containing a map field, I see schemas of the following form:
> {code}
> message: {id: long,events: map[events: int])}}
> {code}
> This same DESCRIBE output does not parse if used within piglatin.

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