Adding new column while CREATE TABLE event trigger fired - postgresql

Question

The goal :
Adding some columns and constraints while creating some tables when the table name begin by "T_R_..."
The code :
CREATE OR REPLACE FUNCTION complete_table()
RETURNS event_trigger
AS
$$
DECLARE
alter_query TEXT;
r RECORD;
BEGIN
IF tg_tag = 'CREATE TABLE'
THEN
r := pg_event_trigger_ddl_commands();
IF r.object_identity LIKE '%.T?_R?_%' ESCAPE '?'
THEN
alter_query = format('ALTER TABLE %s ADD %s_CODE CHAR(16) CONSTRAINT UK_%S_CODE UNIQUE;',
r.object_identity, RIGHT(r.object_identity, 3), RIGHT(r.object_identity, 3));
EXECUTE alter_query;
END IF;
END IF;
END;
$$ LANGUAGE plpgsql;
For the "procedure"... ANd now the trigger :
CREATE EVENT TRIGGER catch_table
ON ddl_command_end
EXECUTE PROCEDURE complete_table();
And finally the test :
CREATE TABLE public.T_R_ABC (ABC_ID INT PRIMARY KEY);
Now, the trouble :
ERROR: ERREUR: la requête « SELECT pg_event_trigger_ddl_commands() » a renvoyé plus d'une ligne
CONTEXT: fonction PL/pgSQL complete_table(), ligne 8 à affectation
Which in english is something like : The query ... returns more than one row ... line 8 when affecting

Answer 1

The function pg_event_trigger_dll_commands() returns several rows: the table itself and the index. You are getting the error that you're getting because you're attempting to assign several rows to a single record. You need to iterate through them and check to make sure you're looking at object_type = 'table'. Also the check for the start of the table name should be case insensitive (ILIKE vs LIKE) and within the format function UK_%S_CODE needs to be UK_%s_CODE (lowercase s):
CREATE OR REPLACE FUNCTION complete_table()
RETURNS event_trigger
LANGUAGE plpgsql
AS $function$
DECLARE
alter_query TEXT;
r RECORD;
BEGIN
IF tg_tag = 'CREATE TABLE'
THEN
FOR r IN SELECT * FROM pg_event_trigger_ddl_commands()
LOOP
IF r.object_type = 'table' and r.object_identity ILIKE '%.T?_R?_%' ESCAPE '?'
THEN
alter_query = format('ALTER TABLE %s ADD %s_CODE CHAR(16) CONSTRAINT UK_%s_CODE UNIQUE;',
r.object_identity, RIGHT(r.object_identity, 3), RIGHT(r.object_identity, 3));
EXECUTE alter_query;
END IF;
END LOOP;
END IF;
END;
$function$;