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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-724) Treating integers and strings in PigStorage
Date Wed, 08 Apr 2009 15:17:12 GMT

    [ https://issues.apache.org/jira/browse/PIG-724?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12697054#action_12697054
] 

Alan Gates commented on PIG-724:
--------------------------------

Currently Pig doesn't require that all keys and values in a map share the same type.  There
is a proposal to change it so that key types can only be chararray (see PIG-734), as we don't
see anyone using anything but chararray and the generality is causing us some other issues.
 But we still wouldn't require that all values in a given map be of the same type.  Are you
proposing allowing users to put a constraint on a given map so that all values in that particular
map must be of that type?

> Treating integers and strings in PigStorage
> -------------------------------------------
>
>                 Key: PIG-724
>                 URL: https://issues.apache.org/jira/browse/PIG-724
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>    Affects Versions: 0.2.1
>            Reporter: Santhosh Srinivasan
>             Fix For: 0.2.1
>
>
> Currently, PigStorage cannot treats the materialized string 123 as an integer with the
value 123. If the user intended this to be the string 123, PigStorage cannot deal with it.
This reasoning also applies to doubles. Due to this issue, maps that contain values which
are of the same type but manifest the issue discussed at beginning of the paragraph, Pig throws
its hands up at runtime.  An example to illustrate the problem will help.
> In the example below a sample row in the data (map.txt) contains the following:
> [key01#35,key02#value01]
> When Pig tries to convert the stream to a map, it creates a Map<Object, Object>
where the key is a string and the value is an integer. Running the script shown below, results
in a run-time error.
> {code}
> grunt> a = load 'map.txt' as (themap: map[]);                    
> grunt> b = filter a by (chararray)(themap#'key01') == 'hello';                  
> grunt> dump b;
> 2009-03-18 15:19:03,773 [main] INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher
- 0% complete
> 2009-03-18 15:19:28,797 [main] ERROR org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher
- Map reduce job failed
> 2009-03-18 15:19:28,817 [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1081: Cannot
cast to chararray. Expected bytearray but received: int
> {code} 
> There are two ways to resolve this issue:
> 1. Change the conversion routine for bytesToMap to return a map where the value is a
bytearray and not the actual type. This change breaks backward compatibility
> 2. Introduce checks in POCast where conversions that are legal in the type checking world
are allowed, i.e., run time checks will be made to check for compatible casts. In the above
example, an int can be converted to a chararray and the cast will be made. If on the other
hand, it was a chararray to int conversion then an exception will be thrown.

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