Postgresql, maintaining hierarchical data with triggers - postgresql

Question

I have adjacency list table account, with columns id, code, name, and parent_id.
To make sorting and displaying easier I added two more columns: depth, and path (materialized path). I know, postgresql has a dedicated data type for materialized path, but I'd like to use a more generic approach, not specific to postgresql. I also applied several rules to my design:
1) code can be up to 10 characters long
2) Max depth is 9; so root account can have sub accounts at maximum 8 level deep.
3) Once set, parent_id is never changed, so there's no need to move a branch of tree to another part of the tree.
4) path is an account's materialized path, which is up to 90 characters long; it is built by concatenating account codes, right padded to 10 characters long; for example, like '10000______10001______'.
So, to automatically maintain depth and path columns, I created a trigger and a trigger function for the account table:
CREATE FUNCTION public.fn_account_set_hierarchy()
RETURNS TRIGGER AS $$
DECLARE d INTEGER; p CHARACTER VARYING;
BEGIN
IF TG_OP = 'INSERT' THEN
IF NEW.parent_id IS NULL THEN
NEW.depth := 1;
NEW.path := rpad(NEW.code, 10);
ELSE
BEGIN
SELECT depth, path INTO d, p
FROM public.account
WHERE id = NEW.parent_id;
NEW.depth := d + 1;
NEW.path := p || rpad(NEW.code, 10);
END;
END IF;
ELSE
IF NEW.code IS DISTINCT FROM OLD.code THEN
UPDATE public.account
SET path = OVERLAY(path PLACING rpad(NEW.code, 10)
FROM (OLD.depth - 1) * 10 + 1 FOR 10)
WHERE SUBSTRING(path FROM (OLD.depth - 1) * 10 + 1 FOR 10) =
rpad(OLD.code, 10);
END IF;
END IF;
RETURN NEW;
END$$
LANGUAGE plpgsql
CREATE TRIGGER tg_account_set_hierarchy
BEFORE INSERT OR UPDATE ON public.account
FOR EACH ROW
EXECUTE PROCEDURE public.fn_account_set_hierarchy();
The above seems to work for INSERTs. But for UPDATEs, an error is thrown: "UPDATE statement on table 'account' expected to update 1 row(s); 0 were matched.". I have a doubt on "UPDATE public.account ..." part. Can someone help me correct the above trigger?

Answer 1

Well, in the above code, update part updates all records, including the record, on which the trigger was fired (concurrency execption?). That seems not to work. So I had to issue 2 different statements:
UPDATE {0}.{1} SET path = OVERLAY(path PLACING rpad(NEW.code, 10)
FROM (OLD.depth - 1) * 10 + 1 FOR 10)
WHERE SUBSTRING(path FROM (OLD.depth - 1) * 10 + 1 FOR 10) = rpad(OLD.code, 10)
AND id <> NEW.id;
NEW.path = OVERLAY(OLD.path PLACING rpad(NEW.code, 10)
FROM (OLD.depth - 1) * 10 + 1 FOR 10);