Postgres trigger to update records of several parent tables based on values of a many-to-many join table referencing those parent table records

Question

I have a PostgreSQL 15 join table schema.m2mjointable to link records of several parent tables (schema.table_a, schema.table_b, ...) with other records of those same parent tables:

id	ref_table	ref_id	rep_table	rep_id
IDENTITY	TEXT	INT	TEXT	INT
----------	--------------	--------	--------------	--------
1	table_a	1	table_a	2
2	table_a	1	table_c	3
3	table_a	4	table_b	7
4	table_b	5	table_a	8
5	table_b	9	table_b	11
6	table_c	7	table_b	11

In the parent tables (schema.table_a, schema.table_b, ...), there is always a boolean field named referenced which should tell if the record i of table n is at least referenced once by the pair of columns ref_table and ref_id in this join table. If that's the case it should be set to TRUE. It should be set to FALSE if it's never present in this pair of columns.

How could I build a trigger function to update the referenced field of the parent tables with such trigger:

CREATE TRIGGER schema.set_referenced_state_biudt
 BEFORE INSERT OR UPDATE OR DELETE
 ON schema.m2mjointable
 FOR EACH ROW EXECUTE PROCEDURE schema.set_referenced_state();

BEGIN;
CREATE OR REPLACE FUNCTION schema.set_referenced_state()
 RETURNS TRIGGER 
 LANGUAGE PLPGSQL
 AS
$$
BEGIN
 -- set the BOOL value of the "referenced" field to TRUE or FALSE
 -- in the record id=value_of(ref_id) of the parent table=value_of(ref_table) 
 -- corresponding to those values of the record being currently inserted/updated/deleted
END;
$$;

Answer 1

Here is what I currently achieved, it's working, but probably not perfect so feel free to improve this idea if you think there are drawbacks:

CREATE OR REPLACE FUNCTION schema.set_referenced_state()
 RETURNS TRIGGER 
 LANGUAGE PLPGSQL
 AS
$$
BEGIN
 IF (TG_OP = 'DELETE') THEN
 EXECUTE format('UPDATE %I.%I SET "referenced" = FALSE WHERE id = 1ドル', TG_TABLE_SCHEMA, OLD.ref_table) USING OLD.ref_id;
 RETURN OLD;
 ELSIF (TG_OP = 'UPDATE' OR TG_OP = 'INSERT') THEN
 EXECUTE format('UPDATE %I.%I SET "referenced" = TRUE WHERE id = 1ドル', TG_TABLE_SCHEMA, NEW.ref_table) USING NEW.ref_id;
 RETURN NEW;
 END IF;
END;
$$;