Re: Suggestion: optionally return default value instead of error on failed cast

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: