Обсуждение: transactions in multiple action rules

Do the multiple actions within a multiple action rule implicitly reside
within a transaction?  I notice that if I brace my multiple actions with
BEGIN; and COMMIT;, that I get a syntax error, so I'm assuming that's
because they are superfluous in that context... ?

(I want to be sure that I can count on 'currval' returning the sequence
value returned by the previous action's 'nextval', so that I know I am
inserting the proper foreign key into a table after inserting a record
into the referenced table.)

--
Ron Peterson
Network & Systems Manager
Mount Holyoke College
http://www.mtholyoke.edu/~rpeterso

On Mon, Dec 20, 2004 at 23:15:39 -0500,
  Ron Peterson <rpeterso@mtholyoke.edu> wrote:
> Do the multiple actions within a multiple action rule implicitly reside
> within a transaction?  I notice that if I brace my multiple actions with
> BEGIN; and COMMIT;, that I get a syntax error, so I'm assuming that's
> because they are superfluous in that context... ?
>
> (I want to be sure that I can count on 'currval' returning the sequence
> value returned by the previous action's 'nextval', so that I know I am
> inserting the proper foreign key into a table after inserting a record
> into the referenced table.)

currval returns the last value given out by nextval in the same session.
So you don't need to worry about conflicts between sessions.

Ron Peterson <rpeterso@mtholyoke.edu> writes:
> Do the multiple actions within a multiple action rule implicitly reside
> within a transaction?

Yes.  In the current code it is actually not possible for a single SQL
command issued by the client to give rise to more than one transaction.
(This might change if we invent some kind of stored-procedure engine, but
rules certainly can't do it.)

> (I want to be sure that I can count on 'currval' returning the sequence
> value returned by the previous action's 'nextval',

As Bruno pointed out, that really has nothing to do with how many
transactions are involved.  The per-session state that currval uses will
sit quietly for as long as you need.

            regards, tom lane