Re: Why can't I put a BEFORE EACH ROW trigger on a view?

Added to TODO:

    * Allow BEFORE INSERT triggers on views

      http://archives.postgresql.org/pgsql-general/2007-02/msg01466.php


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Tom Lane wrote:
> "Karl O. Pinc" <kop@meme.com> writes:
> > why can't I put a SELECT rule on a table?
>
> Because then it would be a view.
>
> As for $SUBJECT, the problem is that there will never be an insert into
> a view --- not at the level of a physical insert attempt anyway --- and
> thus there is nothing for a trigger to do.
>
> The reason there will never be an insertion trigger event is that we
> reject any INSERT on a view that isn't rewritten (by an unconditional
> DO INSTEAD rule) into something else.
>
> I recall a prior discussion about making it possible to use triggers on
> views as a substitute for DO INSTEAD rules, by removing the rewrite-time
> check and only erroring out if we actually get to the point of
> attempting a physical insert.  Then a BEFORE INSERT trigger could do
> something appropriate with the data and return NULL to prevent the
> error.  This seems like a good idea because triggers often are much
> easier to work with than rules --- eg, there's no problem with multiple
> evaluations of volatile functions, even if you send the data to several
> places. However, I'm not sure that the idea scales to cover updates and
> deletes; with no concept of physical tuple identity (ctid) for the view
> rows, it's not clear that you can write triggers that will reliably do
> the right things.
>
>             regards, tom lane
>
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