help with rules please

I dont succeed with writing my rules proper.

I need the following rules:

when I INSERT/UPDATE to a table and a certain condition is true then a
special field in this data-row should be updated to.

I came as far:

# \d testa
Table "public.testa"
Column | Type | Modifiers
--------+------+-----------
x1 | text |
x2 | text |
Rules:
r1 AS
ON INSERT TO testa
WHERE new.x1 = 'house'::text DO UPDATE testa SET x2 = 'mouse'::text

this works fine. When I insert a row with x1=house then x2 gets set to
mouse.

BUT:

i) it always updates all rows in the tables instead of only the current
row. I guess this is a huge performance-lack on big tables :) I tried
to get a where oid=new.oid in or something like that, but it did not work.

ii) the above rule does not work on UPDATE, cause I get a deep
recursion. Each update causes another update on the same table which
makes postgres break with a nested.loop -error (happily postgres detects
the recursion :)

thnx for any help
peter

--
mag. peter pilsl
goldfisch.at
IT- & dataconsulting
tel: +43 650 3574035
tel: +43 1 8900602
fax: +43 1 8900602 15
pilsl(at)goldfisch(dot)at