Triggers in Postgres: Access NEW fields by name at runtime - postgresql

Question

In Postgres, someone knows how to substitute the value of the variable in a NEW.variable in a trigger?
For instance, I have a variable with value order_code. I want to execute NEW.variable so that it's getting in fact NEW.order_code.
In detailed:
I have a function to obtain the primary key column of a table:
CREATE FUNCTION getPrimaryKey(_table_name VARCHAR(50))
RETURNS SETOF VARCHAR(50) AS $$
DECLARE
primary_key VARCHAR(50);
BEGIN
FOR primary_key IN SELECT a.attname
FROM pg_index i
JOIN pg_attribute a ON a.attrelid = i.indrelid
AND a.attnum = ANY(i.indkey)
WHERE i.indrelid = _table_name::regclass
AND i.indisprimary LOOP
RETURN NEXT primary_key;
END LOOP;
END;
$$ LANGUAGE plpgsql;
Then I have a trigger to collect some info when an INSERT is done in a table. The procedure in the trigger is called from several triggers from different tables. That's why it's so generic and I have this need.
What I want is to obtain the primary key of the object inserted.
CREATE FUNCTION logAudit()
RETURNS trigger AS $$
DECLARE primary_key VARCHAR(50);
BEGIN
primary_key := getprimarykey(TG_TABLE_NAME::VARCHAR(50));
INSERT INTO test VALUES (TG_TABLE_NAME);
INSERT INTO test VALUES (NEW.primary_key);
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER audit_in_client
AFTER INSERT ON tb_client
FOR EACH STATEMENT EXECUTE PROCEDURE logAudit();
The NEW.primary_key is what is causing me issues. I expect primary_key to be the column name of the source table where the insert happened. What I want in NEW.primary_key is to actually use the value in the variable.

Answer 1

Here is the example of anonymous pl/pgsql block which doing something what you want:
do $$
declare
v pg_database = (pg_database) from pg_database where datname = 'template1';
fname text = 'datname';
n text;
begin
n := to_jsonb(v)->>fname;
raise info '%', n;
end $$;
Output:
INFO: template1
It is working example. In your trigger function it could be something like
declare
pk_name text;
pk_value text;
begin
pk_name := getprimarykey(TG_TABLE_NAME::VARCHAR(50));
pk_value := to_jsonb(NEW) ->> pk_name;
-- Do what you want with pk_value here
return null;
end $$;