postgresql - Postgres plpgsql JSON assignment -

i'm working jsonb in postgres , trying understand how correctly perform assignment json property in plpgsql.

this query snippet reports syntax error because of leading bracket on assignment, sure syntax required refer json objects in plpgsq:

if (new."data")->>'custom' null   (new."data")->>'custom' := 0; end if; 

this in postgresql trigger, new provided variable relating new database record.

can advise correct technique assigning value json(b) property?

in postgres 9.5 quite simple function jsonb_set():

if new.data->>'custom' null     new.data = jsonb_set(new.data::jsonb, '{custom}', '0'::jsonb); end if; 

there no jsonb_set() in postgres 9.4 issue more complicated:

if new.data->>'custom' null     new.data = (         select json_object_agg(key, value)         (             select key, value             jsonb_each(new.data)             union             values ('custom', '0'::jsonb)         ) s     ); end if;