aoa how can i connect my postgres database to manifold? Regards?
On Fri, Aug 6, 2010 at 12:49 PM, Dean Rasheed <dean.a.rash...@gmail.com>wrote: > On 4 August 2010 15:08, Marko Tiikkaja <marko.tiikk...@cs.helsinki.fi> > wrote: > > On 8/4/10 5:03 PM +0300, Dean Rasheed wrote: > >> > >> On 4 August 2010 14:43, Marko Tiikkaja<marko.tiikk...@cs.helsinki.fi> > >> wrote: > >>> > >>> I'm not sure I understand. RETURNING in DELETE on a table fetches the > >>> old > >>> value after it was DELETEd, so it really is what the tuple was before > the > >>> DLETE, not what is seen by the snapshot. In a BEFORE DELETE trigger, > the > >>> row is always locked so it can't change after the trigger is fired. > >>> > >> > >> Ah, I think I mis-understood. If I understand what you're saying > >> correctly, you're worried that the row might have been modified in the > >> same query, prior to being deleted, and you want RETURNING to return > >> the updated value, as it was when it was deleted. > > > > I'm mainly concerned about concurrently running transactions. > > > > Sorry for the delay replying. > > Once again, I think I mis-understood your point. I think that the > database can't really lock anything before firing the trigger because > the view might contain grouping/aggregates or even not be based on any > real tables at all, so it would be impossible to work out what to > lock. Thus it would be up to the trigger function to get this right. > In the simplest case, for a DELETE, this might look something like: > > CREATE OR REPLACE FUNCTION instead_of_delete_trig_fn() > RETURNS trigger AS > $$ > BEGIN > DELETE FROM base_table WHERE pk = OLD.pk; > IF NOT FOUND THEN RETURN NULL; END IF; > > RETURN OLD; > END; > $$ > LANGUAGE plpgsql; > > If 2 users try to delete the same row, the second would block until > the first user's transaction finished, and if the first user > committed, the second user's trigger would return NULL, which the > database would signal as no rows deleted. > > Regards, > Dean > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers >
