On Thu, Jan 6, 2022 at 12:18 PM Andrew Dunstan <and...@dunslane.net> wrote:
> > On 1/4/22 22:17, Corey Huinker wrote: > > > > currently a failed cast throws an error. It would be useful to have a > > way to get a default value instead. > > > > > > I've recently encountered situations where this would have been > > helpful. Recently I came across some client code: > > > > CREATE OR REPLACE FUNCTION is_valid_json(str text) RETURNS boolean > > LANGUAGE PLPGSQL > > AS $$ > > DECLARE > > j json; > > BEGIN > > j := str::json; > > return true; > > EXCEPTION WHEN OTHERS THEN return false; > > END > > $$; > > > > > > This is a double-bummer. First, the function discards the value so we > > have to recompute it, and secondly, the exception block prevents the > > query from being parallelized. > > > This particular case is catered for in the SQL/JSON patches which > several people are currently reviewing: > > That's great to know, but it would still be parsing the json twice, once to learn that it is legit json, and once to get the casted value. Also, I had a similar issue with type numeric, so having generic "x is a type_y" support would essentially do everything that a try_catch()-ish construct would need to do, and be more generic.
