To: pgsql-sql@postgresql.org
From: Wiebe Cazemier <halfgaar@gmx.net>
Subject: Re: Delete rules and functions
Date: Tue, 26 Jun 2007 23:37:11 +0200
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References: <f5rpk6$r8n$1@sea.gmane.org> <28442.1182891012@sss.pgh.pa.us>
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On Tuesday 26 June 2007 22:50, Tom Lane wrote:

> Please provide an example, because the rewriter is most certainly
> applied to queries from functions.
> 
> I suspect you are actually being burnt by some other effect, like a row
> disappearing from the view as soon as its underlying data is deleted.

Here is an example (and it's nothing more than an example...):

--------------

CREATE TABLE cars
(
  id SERIAL PRIMARY KEY
);

--------------

CREATE TABLE car_parts
(
  id SERIAL PRIMARY KEY,
  car_id INTEGER NOT NULL REFERENCES cars ON DELETE CASCADE,
  steering_wheel_id INTEGER NOT NULL REFERENCES steering_wheels
);

--------------

CREATE RULE AS ON DELETE TO car_parts DO ALSO
(
  DELETE FROM steering_wheels WHERE id = OLD.steering_wheel_id;
);

--------------

CREATE VIEW cars_view AS SELECT * FROM cars;

--------------

CREATE FUNCTION cars_delete(p_old) RETURNS VOID AS $$
BEGIN
  DELETE FROM cars where id = p_old.id;
END;
$$ LANGUAGE plpgsql;

--------------

CREATE RULE AS ON DELETE TO cars_view DO INSTEAD
(
  SELECT cars_delete();
);

--------------

Now, when I delete a row from the cars_view, the underlying record from car is
deleted, which cascades to car_parts. The rule intended for removing the
steering wheel doesn't do anything.

And now that I wrote it, I can see that it's indeed because OLD no longer
exists. I knew this was the case for rules, but I overlooked it, apparently...

I had already converted it to use triggers, and I'll leave it that way.