Обсуждение: Rules and sequences

I am trying to implement a fairly standard 'audit table' setup, but
using rules instead of triggers (since it should be more efficient).
However, I'm running into problems when one of the audited tables has a
'serial' column that is allowed to default:
   create table foo (id serial, bar text);   create table audit (ix bigserial, rec text);   create rule audit_insert as
oninsert to foo do also        insert into audit (rec) values ((new.*)::text);   insert into foo (bar) values ('baz');
select * from foo;        id | bar        ----+-----         1 | baz       (1 row)   select * from audit;        ix |
rec         ----+---------         1 | (2,baz)       (1 row)
 

I can see why this is happening (the rule is essentially a macro, so the
NEW expression gets expanded twice, including the nextval call, so the
sequence is incremented twice), but is there any way to prevent it? Some
way of 'materialising' the NEW row so it is just plain values rather
than a list of expressions?

Ben

Ben Morrow <ben@morrow.me.uk> writes:
> I am trying to implement a fairly standard 'audit table' setup, but
> using rules instead of triggers (since it should be more efficient).

Rules are sufficiently tricky that I would never, ever rely on them for
auditing.  Use a simple AFTER trigger instead.
        regards, tom lane

In response to Tom Lane :
> Ben Morrow <ben@morrow.me.uk> writes:
> > I am trying to implement a fairly standard 'audit table' setup, but
> > using rules instead of triggers (since it should be more efficient).
> 
> Rules are sufficiently tricky that I would never, ever rely on them for
> auditing.  Use a simple AFTER trigger instead.

There are a ready solution:
http://andreas.scherbaum.la/blog/archives/100-Log-Table-Changes-in-PostgreSQL-with-tablelog.html


Regards, Andreas
-- 
Andreas Kretschmer
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Quoth tgl@sss.pgh.pa.us (Tom Lane):
> Ben Morrow <ben@morrow.me.uk> writes:
> > I am trying to implement a fairly standard 'audit table' setup, but
> > using rules instead of triggers (since it should be more efficient).
> 
> Rules are sufficiently tricky that I would never, ever rely on them for
> auditing.  Use a simple AFTER trigger instead.

OK, thanks. 

Ben