[ADMIN] custom cast for to_json()

CREATE or replace FUNCTION mytimecast(val timestamp with time zone) RETURNS json AS $$

BEGIN

RETURN to_json(to_char(val, 'YYYY-MM-DD"T"HH24:MI:SS.MSZ'));

END; $$

LANGUAGE PLPGSQL;

--custom cast that uses the above user defined function 

create cast (timestamp with time zone AS json ) with function mytimecast (timestamp with time zone) AS IMPLICIT;

Direct cast to json uses the custom cast and returns the formatted date time from the user defined function:

select now()::json;

            now            

----------------------------

"2017-08-31T13:01:04.782Z"

However, to_json() function didn't use the custom cast and returning the default UTC format:

select to_json(now());

              to_json              

------------------------------------

"2017-08-31T13:01:18.474781+00:00"