Обсуждение: Getting the typename of a polymorphic function's magical $0 variable

Hello,

I've written the following function:

CREATE OR REPLACE FUNCTION indifferent_cast(literal_value text,
type_specification anyelement) RETURNS anyelement AS
$function_body$
-- This function is used when writing migrating scripts and the like.
-- It attempts to cast to the datatype specified by
"type_specification", but, in the event of the cast
-- being unsuccessfuly, it swallows the error and returns NULL

-- example of usage:
-- select indifferent_cast('5391502794050'::text, NULL::gtin)

-- It's useful for migrating data from legacy systems without
appropriate integrity constraints, where a small
-- minority of a particularly field of data will not cast to a desired
datatype (particularly a domain with a check constraint),
-- and you're quite happy to lose this data rather than relax your
constraints or manually correct the legacy data, or you cannot
-- be reasonably expected to correct the malformed data ( as, perhaps,
in the case of a malformed GTIN barcode)

-- It's called indifferent_cast for a reason

-- Clearly, creating a regular cast through CREATE CAST isn't
appropriate for this

DECLARE

BEGIN
    $0 := $1;
    return $0;

EXCEPTION
            WHEN others THEN
                RAISE NOTICE 'Failed to perform indifferent_cast';
                RETURN NULL;

END;

$function_body$
LANGUAGE 'plpgsql' IMMUTABLE

I would like to be able to RAISE a more appropriate, business domain
level notice, such as 'could not validate barcode' or 'could not
validate e-mail address', based on a CASE statement that checks the
dynamic type of $0 against some likely candidates for my application.

Is it possible to do this? How?

Thanks,
Peter Geoghegan

Hello

you can use pg_typeof(some) function

Regards
Pavel Stehule

2010/4/22 Peter Geoghegan <peter.geoghegan86@gmail.com>:
> Hello,
>
> I've written the following function:
>
> CREATE OR REPLACE FUNCTION indifferent_cast(literal_value text,
> type_specification anyelement) RETURNS anyelement AS
> $function_body$
> -- This function is used when writing migrating scripts and the like.
> -- It attempts to cast to the datatype specified by
> "type_specification", but, in the event of the cast
> -- being unsuccessfuly, it swallows the error and returns NULL
>
> -- example of usage:
> -- select indifferent_cast('5391502794050'::text, NULL::gtin)
>
> -- It's useful for migrating data from legacy systems without
> appropriate integrity constraints, where a small
> -- minority of a particularly field of data will not cast to a desired
> datatype (particularly a domain with a check constraint),
> -- and you're quite happy to lose this data rather than relax your
> constraints or manually correct the legacy data, or you cannot
> -- be reasonably expected to correct the malformed data ( as, perhaps,
> in the case of a malformed GTIN barcode)
>
> -- It's called indifferent_cast for a reason
>
> -- Clearly, creating a regular cast through CREATE CAST isn't
> appropriate for this
>
> DECLARE
>
> BEGIN
>        $0 := $1;
>        return $0;
>
> EXCEPTION
>                        WHEN others THEN
>                                RAISE NOTICE 'Failed to perform indifferent_cast';
>                                RETURN NULL;
>
> END;
>
> $function_body$
> LANGUAGE 'plpgsql' IMMUTABLE
>
> I would like to be able to RAISE a more appropriate, business domain
> level notice, such as 'could not validate barcode' or 'could not
> validate e-mail address', based on a CASE statement that checks the
> dynamic type of $0 against some likely candidates for my application.
>
> Is it possible to do this? How?
>
> Thanks,
> Peter Geoghegan
>
> --
> Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-general
>

> Hello
>
> you can use pg_typeof(some) function
>
> Regards
> Pavel Stehule

That's great Pavel, thanks a lot.

Regards,
Peter Geoghegan