Why should my rule be conditional?

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Hi,

I have a view that I want to make updateble, at least kind of. What should
happen on update (trying to implement in one rule):
- - make the original record invisible in the view by changing the value of a
flag in the table underlying table
- - insert a new record into the underlying table
- - update another table (I have not come that far)

Therefore I created following rule:
CREATE OR REPLACE RULE r_v_songs_upd
   AS ON UPDATE TO v_songs
   DO INSTEAD (
      UPDATE t_songs
         SET
            show = FALSE
         WHERE
            NEW.song_id = song_id
      ;
      INSERT INTO t_songs (
            song_title,
            year_of_composition,
            year_of_first_publication,
            predecessor_id
         ) VALUES (
            NEW.song_title,
            NEW.year_of_composition,
            NEW.year_of_first_publication,
            NEW.song_id
         )
   )
;

If I do the update on v_songs, the update part of the rule gets executed fine,
but the insert does not seem to do anything. So I changed to the rule for
testing into:
CREATE OR REPLACE RULE r_v_songs_upd
   AS ON UPDATE TO v_songs
   DO INSTEAD (
      UPDATE t_songs
         SET
            show = FALSE
         WHERE
            NEW.song_id = song_id
      ;
      INSERT INTO t_songs (
            song_title,
            year_of_composition,
            year_of_first_publication,
            predecessor_id
         ) VALUES (
'rübenkraut',1,2,null
         )
   )
;

An update now results in:
psql:data.pgsql:124: ERROR:  Cannot update a view
        You need an unconditional ON UPDATE DO INSTEAD rule

Why? I cannot see where my rule is some kind of conditional. I couldn't find
any hint, neither in the docs, nor googling, nor metacrawling.

Anybody an idea?

Cheers

Thiemo

- --
root ist die Wurzel allen Übels
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