Hello all,
I tried to implement the following rule: if someone wants to delete a record
from a table t_xyz (id integer, deleted boolean) the record should get a
delete-flag (deleted = true). When this "pre-deleted" record is deleted for
the next time it should be physically deleted from the database.
I implemented the following rule:
CREATE RULE r_del_xyz
AS ON DELETE TO t_xyz WHERE (old.deleted = false)
DO INSTEAD
UPDATE t_xyz
SET deleted = true
WHERE id = old.id;
Now I tested the new rule:
INSERT INTO t_xyz VALUES (1, false);
INSERT INTO t_xyz VALUES (2, false);
DELETE FROM t_xyz WHERE id = 1;
SELECT * FROM t_xyz ;
id | deleted
----+---------
2 | f
What has happened? The rule seems to be ignored and the record was deleted!
I dropped the rule, deleted all records and recreated the rule without the
additional WHERE-Clause in the UPDATE-Statement:
DROP RULE r_del_xyz;
DELETE FROM t_xyz;
CREATE RULE r_del_xyz
AS ON DELETE TO t_xyz WHERE (old.deleted = false)
DO INSTEAD
UPDATE t_xyz
SET deleted = true;
INSERT INTO t_xyz VALUES (1, false);
INSERT INTO t_xyz VALUES (2, false);
The same test again:
DELETE FROM t_xyz WHERE id = 1;
SELECT * FROM t_xyz ;
id | deleted
----+---------
2 | t
It seems to me that PostgreSQL executed the rule, but ignored the keyword
INSTEAD and deleted the record after having updated it?!
One last test with a slightly different rule (look at the WHERE-clause in
the "AS-ON"-clause):
DROP RULE r_del_xyz;
DELETE FROM t_xyz;
CREATE RULE r_del_xyz
AS ON DELETE TO t_xyz WHERE (1 = 1)
DO INSTEAD
UPDATE t_xyz
SET deleted = true
WHERE id = old.id;
INSERT INTO t_xyz VALUES (1, false);
INSERT INTO t_xyz VALUES (2, false);
DELETE FROM t_xyz WHERE id = 1;
SELECT * FROM t_xyz ;
id | deleted
----+---------
2 | f
1 | t
DELETE FROM t_xyz WHERE id = 1;
SELECT * FROM t_xyz ;
Everything is alright now! Am I wrong? Is the WHERE-clause "WHERE
(old.deleted = false)" not correct? Any hints? Or it is really a bug?
Best regards, Jens Hartwig
PS: You will find the scripts in the attachment.
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rule_error_1.sql
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rule_error_3.sql
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