Re: OLD pseudo relation for INSERT in rules and triggers

On 01/01/2013 10:17 AM, Rafał Pietrak wrote:
> Hello the list,
>
> As far as I can tell from a quick search through postgresql
> documentation, the OLD.* pseudorelation is not available for INSERT
> triggers and rules. And a little googleing I did, haven't pointed me to
> anything relevant to the following. My apology if I miss in my search
> such discussion happening earlier (I apreciate a pointer, where I can
> see pros and cons that've been raisen back then);
>
> If not, I think having OLD.* in INSERT rules/triggers is worth pondering.
>
> The thing is, that it would be a valuable tool to mimic table-propper
> functionality by a view. The OLD.* preudorelation on INSERT could
> provide column defaults from the underlaying table definition.
>
> like:
> CREATE TABLE test (tm timestamp default now(), info text);
> CREATE TABLE test_view AS SELECT * FROM test;
> CREATE RULE with_defaults AS ON INSERT to test_view DO INSTEAD INSERT
> INTO test (tm,info) VALUES ( //COALESCE(NEW.tm, OLD.tm), NEW.text);
>
> so:
> INSERT INTO test_view (info) VALUES ('hello');
> and:
> INSERT INTO test_view (tm, info) VALUES (null, 'hello');
>
> both work just as if test_view was a TABLE with a default tm value defined.

http://www.postgresql.org/docs/9.2/interactive/sql-alterview.html

"SET/DROP DEFAULT
These forms set or remove the default value for a column. A default
value associated with a view column is inserted into INSERT statements
on the view before the view's ON INSERT rule is applied, if the INSERT
does not specify a value for the column."

It is not quite the same, but close.

>
> -R

--
Adrian Klaver
adrian(dot)klaver(at)gmail(dot)com