Thread: filtering columns in function

i have several APIs which operate over several different tables. first allow me to show you some plpgsql i use, this is semantically the same in all of my APIs with different names for tables (this is python generating the SQL statements):

            _proc = '''

                CREATE OR REPLACE FUNCTION notify_proc() RETURNS trigger AS $$

                DECLARE

                    _json    json;

                    _record  record;

                BEGIN

                    IF TG_OP = 'INSERT' or TG_OP = 'UPDATE' THEN

                        SELECT TG_TABLE_NAME AS table, TG_OP AS action, NEW.*

                        INTO    _record;

                    ELSE

                        SELECT TG_TABLE_NAME AS table, TG_OP AS action, OLD.*

                        INTO    _record;

                    END IF;

                    _json = row_to_json(_record);

                    PERFORM pg_notify(CAST('dfw' AS text), CAST(_json AS text));

                    IF TG_OP = 'INSERT' or TG_OP = 'UPDATE' THEN

                        RETURN NEW;

                    ELSE

                        RETURN OLD;

                    END IF;

                END;

                $$ LANGUAGE plpgsql;

                '''

            _trig = '''

                DO

                $$

                BEGIN

                    IF NOT EXISTS (SELECT *

                        FROM  information_schema.triggers

                        WHERE event_object_table = '{table}'

                        AND   trigger_name = 'dfw_notify_{table}_{op}'

                    )

                    THEN

                        CREATE TRIGGER dfw_notify_{table}_{op} {when} {op}

                                    ON {table}

                          FOR EACH ROW

                               EXECUTE

                             PROCEDURE notify_proc();

                    END IF;

                END;

                $$

                '''

            c.execute(_proc)

            for table in {'blocklist','recents','filter_meta','filter_whitelist'}:

                for op,when in {'insert':'BEFORE','update':'AFTER','delete':'BEFORE'}.items():

                    c.execute(_trig.format(op=op, when=when, table=table))

because i use this approach frequently for a number of software packages, i'd like to improve on it. pg notifications have a fixed size limit and recently i'm encountering more and more notifications are lost because this size limit is reached -- PG will emit an error instead of performing the notification. some of my databases have dozens of different tables with all sorts of different columns that i use this trigger and function on.

with the background provided, here's the question; without making a complex series of table name if/else stanzas, how can i more succinctly change my select query to omit certain columns?

                    IF TG_OP = 'INSERT' or TG_OP = 'UPDATE' THEN

                        SELECT TG_TABLE_NAME AS table, TG_OP AS action, NEW.*

                        INTO    _record;

                    ELSE

                        SELECT TG_TABLE_NAME AS table, TG_OP AS action, OLD.*

                        INTO    _record;

                    END IF;

in other words, instead of NEW.* or OLD.*, i'd like to do NEW.* EXCLUDING ('somecol1','somecol2')