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
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