Message-ID: <2b698dcbd606bf8c5afec14ef159d16a1b7270ea.camel@cybertec.at>
Subject: Re: Cascade rules on INSERT wrong behaviour on 16.0
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Oleksandr Voytsekhovskyy <young.inbox@gmail.com>,
	pgsql-bugs@lists.postgresql.org
Date: Wed, 31 Jan 2024 16:52:20 +0100
In-Reply-To: <9753FA5E-5AC8-4446-B335-70A215447026@gmail.com>
References: <9753FA5E-5AC8-4446-B335-70A215447026@gmail.com>
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On Wed, 2024-01-31 at 14:44 +0100, Oleksandr Voytsekhovskyy wrote:
> CREATE TABLE first (
> =C2=A0 =C2=A0 id uuid DEFAULT gen_random_uuid() PRIMARY KEY
> );
>=20
> CREATE TABLE second (
> =C2=A0 =C2=A0 first_id uuid,
> =C2=A0 =C2=A0 second_id uuid
> );
>=20
> CREATE TABLE third (
> =C2=A0 =C2=A0 second_id uuid
> );
>=20
> CREATE RULE first_insert AS ON INSERT TO first DO ALSO
> INSERT INTO second VALUES (NEW.id, gen_random_uuid());
>=20
> CREATE RULE second_insert AS ON INSERT TO second DO ALSO
> INSERT INTO third VALUES (NEW.second_id);
>=20
> test=3D# insert into first values ('9ea8e702-421c-45d5-842f-a81dc3848022'=
);
> INSERT 0 1
> test=3D# select * from second;
> =C2=A0=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 first_id =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 second_id=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0
> --------------------------------------+----------------------------------=
----
> =C2=A09ea8e702-421c-45d5-842f-a81dc3848022 | 8c601583-df70-47fd-b748-7dc4=
a5bc9f75
> (1 row)
>=20
> test=3D#=C2=A0 select* from third;
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 second_id=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0
> --------------------------------------
> =C2=A0848919c7-de3d-4635-bf3a-07d200cb2792
> (1 row)
>=20
>=20
> I expect that values of second_id from the table second and third will be=
 the same, but in fact they are different.

That is expected, and that's how rules work.

If you don't want that, you should use triggers, which are working
in a less surprising fashion.

Yours,
Laurenz Albe