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.
