Re: Rules with Conditions: Bug, or Misunderstanding

Tom Lane wrote:
> "Joel Burton" <jburton(at)scw(dot)org> writes:
> > create rule dev_ins as on update to dev_col_comments where
> > old.description isnull do instead insert into pg_description ( objoid,
> > description) values (old.att_oid, new.description);
>
> > create rule dev_upd as on update to dev_col_comments where
> > old.description notnull do instead update pg_description set
> > description=new.description where objoid=old.att_oid;
>
> > This doesn't work: I get a "cannot update view w/o rule" error
> > message, both for fields where description was null, and for fields
> > where it wasn't null.
>
> Hm. Perhaps the "cannot update view" test is too strict --- it's not
> bright enough to realize that the two rules together cover all cases,
> so it complains that you *might* be trying to update the view. As the
> code stands, you must provide an unconditional DO INSTEAD rule to
> implement insertion or update of a view.

Disagree.

A conditional rule splits the command into two, one with the
rules action and the condition added, one which is the
original statement plus the negated condition. So there are
cases left where an INSERT can happen to the view relation
and it's the job of this test to prevent it.

Jan

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