[jira] [Commented] (PIG-3082) outputSchema of a UDF allows two usages when describing a Tuple schema

["Julien Le Dem (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PIG-3082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13556686#comment-13556686 ] 

Julien Le Dem commented on PIG-3082:
------------------------------------

Thanks for fixing Jon!
I find the error message a little confusing:
{noformat}
 throw new FrontendException("Given UDF returns an improper Schema. Should only return Tuple, Bag, or a single item. Returns: " + udfSchema);
{noformat}
It should contain something along the lines of "... outputSchema should return a Schema containing a single Field ...".
Otherwise, it looks good to me.
Thanks
                
> outputSchema of a UDF allows two usages when describing a Tuple schema
> ----------------------------------------------------------------------
>
>                 Key: PIG-3082
>                 URL: https://issues.apache.org/jira/browse/PIG-3082
>             Project: Pig
>          Issue Type: Bug
>            Reporter: Julien Le Dem
>            Assignee: Jonathan Coveney
>             Fix For: 0.12
>
>         Attachments: PIG-3082-0.patch
>
>
> When defining an evalfunc that returns a Tuple there are two ways you can implement outputSchema().
> - The right way: return a schema that contains one Field that contains the type and schema of the return type of the UDF
> - The unreliable way: return a schema that contains more than one field and it will be understood as a tuple schema even though there is no type (which is in Field class) to specify that. This is particularly deceitful when the output schema is derived from the input schema and the outputted Tuple sometimes contain only one field. In such cases Pig understands the output schema as a tuple only if there is more than one field. And sometimes it works, sometimes it does not.
> We should at least issue a warning (backward compatibility) if not plain throw an exception when the output schema contains more than one Field.

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