Subject: Re: Example 42.4. A PL/pgSQL Trigger Function for Auditing

From: PG Doc comments form <[email-masked]>
Date: Sun, 15 Dec 2019 22:35:17 +0000

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/12/plpgsql-trigger.html
Description:

I'm wondering if it would be worthwhile to put a totally generic auditing
function into the documentation e.g.

CREATE OR REPLACE FUNCTION zz_audit_() RETURNS TRIGGER AS $nothing$

-- This function is intended to be used by a delete/insert/update trigger
for any table.
-- It relies on the existence of a table named zz_audit_XXX (where XXX is
the table being audited) that contains the
-- same columns as the table XXX except that two additional columns must
exist prior to the columns from XXX
--    operation character(1) NOT NULL,
--    tstamp    timestamp with time zone NOT NULL,
--    ...       remaining columns per table XXX

    DECLARE audit_table_name NAME := CONCAT('zz_audit_', TG_TABLE_NAME);
    BEGIN
		
        IF (TG_OP = 'DELETE') THEN
            EXECUTE 'INSERT INTO ' || audit_table_name || ' SELECT ''D'',
now(), ' || ' $1.*' USING OLD;
        ELSIF (TG_OP = 'UPDATE') THEN
			EXECUTE 'INSERT INTO ' || audit_table_name || ' SELECT ''U'', now(), ' ||
' $1.*' USING NEW;
        ELSIF (TG_OP = 'INSERT') THEN
			EXECUTE 'INSERT INTO ' || audit_table_name || ' SELECT ''I'', now(), ' ||
' $1.*' USING NEW;
        END IF;

        RETURN NULL; -- result is ignored since this is an AFTER trigger
    END;
$nothing$ LANGUAGE plpgsql;

---

From: Pavel Stehule <[email-masked]>
Date: Mon, 16 Dec 2019 12:25:34 +0100

> $nothing$ LANGUAGE plpgsql;

Just few points to this code

1. bad, useless brackets in IF .. ELSIF expressions - plpgsql is not C or
Java
2. unescaped identifiers in dynamic SQL - EXECUTE
3. there is not reason for INSERT SELECT.

Regards

Pavel

---

From: Tom Lane <[email-masked]>
Date: Mon, 16 Dec 2019 14:27:58 -0500

Pavel Stehule <[email-masked]> writes:
>> [ snip ]

> Just few points to this code

I agree this code could have better style, but maybe that is just more
evidence that a well-written example would be helpful?

			regards, tom lane

---

From: Daniel Gustafsson <[email-masked]>
Date: Mon, 16 Dec 2019 20:35:22 +0100

> On 16 Dec 2019, at 20:27, Tom Lane <[email-masked]> wrote:
> 
> .. maybe that is just more

I think thats the key takeaway here.  +1 on the gist of the suggestion that
started this thread.

cheers ./daniel

---

From: Pavel Stehule <[email-masked]>
Date: Mon, 16 Dec 2019 20:42:04 +0100

> evidence that a well-written example would be helpful?

+1

there is not too much examples for trigger parameters.