conditional rule not applied

[Seb <spluque@xxxxxxxxx>]

Hi,

I'm trying to create a rule to be applied on update to a view that
consists of two joined tables.  Table 'shoes' below is left-joined with
table 'shoelaces' in the view 'footwear'.  I'd like to create a simple
update rule on the view, only if the value of a common column
corresponds to an inexistent record in 'shoelaces', so the result is an
INSERT into 'shoelaces' with the new record:

---<--------------------cut here---------------start------------------->---
CREATE TABLE shoes (
	sh_id serial PRIMARY KEY,
	sh_name text,
	sh_avail integer
);

CREATE TABLE shoelaces (
	sl_id serial PRIMARY KEY,
	sh_id integer REFERENCES shoes,
	sl_name text
);

INSERT INTO shoes (sh_name, sh_avail)
    VALUES ('sh1', 2), ('sh2', 0), ('sh3', 4), ('sh4', 3);

INSERT INTO shoelaces (sh_id, sl_name)
    VALUES (1, 'sl1'), (3, 'sl2');

SELECT * FROM shoes;

 sh_id | sh_name | sh_avail 
-------+---------+----------
     1 | sh1     |        2
     2 | sh2     |        0
     3 | sh3     |        4
     4 | sh4     |        3

SELECT * FROM shoelaces;

 sl_id | sh_id | sl_name 
-------+-------+---------
     1 |     1 | sl1
     2 |     3 | sl2
(2 rows)

CREATE VIEW footwear AS
SELECT sh.sh_id, sh_name, sh_avail, sl_name
FROM shoes sh LEFT JOIN shoelaces sl USING (sh_id);

SELECT * FROM footwear;

 sh_id | sh_name | sh_avail | sl_name 
-------+---------+----------+---------
     1 | sh1     |        2 | sl1
     2 | sh2     |        0 | 
     3 | sh3     |        4 | sl2
     4 | sh4     |        3 | 
(4 rows)

CREATE RULE footwear_nothing_upd AS
    ON UPDATE TO footwear DO INSTEAD NOTHING;
CREATE RULE footwear_newshoelaces_upd AS
    ON UPDATE TO footwear
    WHERE NEW.sl_name <> OLD.sl_name AND OLD.sl_name IS NULL
    DO
INSERT INTO shoelaces (sh_id, sl_name)
    VALUES(NEW.sh_id, NEW.sl_name);

-- Testing: result should be a new record in 'shoelaces'
UPDATE footwear SET sl_name = 'sl3' WHERE sh_name = 'sh2';

-- but that doesn't happen:
SELECT * FROM shoelaces;

 sl_id | sh_id | sl_name 
-------+-------+---------
     1 |     1 | sl1
     2 |     3 | sl2
(2 rows)
---<--------------------cut here---------------end--------------------->---

Any tips would be much appreciated.

-- 
Seb


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