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
REFERENCESsteering_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.
