Re: Triggers and SQL functions

pierre(at)desertmoon(dot)com wrote:
>
> >
> > I have exactly the same problem as you mentioned in a mail
> > sent to postgres mailing lists about creating trigger using
> > sql function ...
> >
> > Did you get the solution to you problem ?
> >
> > Ph.R.
> >
> >
>
> I actually found the solution in the docs. The solution is to understand
> the difference between triggers and rules. Triggers are used primarily
> to call C/C++ library functions that you can create and add onto the
> postgresql system.
>
> Rules on the other-hand act just like 'triggers' but only call/usr
> sql to perform their functions.
>
> So the solution: Use rules to create trigger-like actions that run
> stored sql procedures. There is a man page on 'create rule' that you
> can use to get more info.
>
> -=pierre

The problem is the following:

CREATE TABLE user (
id int,
username char(10),
passwd char(10)
);
CREATE sequence user_seq start 1 increment 1;
CREATE RULE adduser as
on insert to user where id isnull
do update user set id=nextval('user_seq') where id isnull;
--
As you can see, I implement kind of autoinc on id.

CREATE TABLE user_realm (
uid int,
rlid int,
adminuser boolean
);

I would like to defaultly add a user in the realm 1.
I tried the following:
CREATE RULE adduservoid as
on insert to user
do insert into user_realm values(new.id, 1, false);

But new.id is very probably null !
The problem is that rules is a rewriting system and not function calls
(and so no way to define after/befor).
So I would like to do this auto-insert into user_realm with a trigger
after insert. I tried the following :

-- Makes all user at least belonging to Void ... just in case
CREATE FUNCTION adduservoid () returns boolean
as 'insert into user_realm
select id as uid,1 as rlid,false as adminuser
from user where not exists (
select uid from user_realm where user.id=user_realm.uid
);
select true as ignore_this;'
language 'sql';
CREATE TRIGGER autoadduservoid AFTER INSERT OR UPDATE ON user for each
row
EXECUTE PROCEDURE adduservoid();

But this doesnt work for the reason you mentioned.
Another solution would be if the create rule would support many
statements instead of just one, like that:
CREATE RULE adduser as
on insert to user where id isnull
do 'update user set id=nextval('user_seq') where id isnull;
insert into user_realm(new.id,1,false);'

But because I have also a check_primary key on user_realm that ensure
that uid exists in user ... I would still have a problem !

Ph.R.

--
_____________________________________________________________________
Philippe Rochat, EPFL DI-LBD
Database Laboratory CH-1015 LAUSANNE
Swiss Federal Institute of Technology (EPFL) tel:++41 21 693 52 53
Beep-EPFL: 181 4644 fax:++41 21 693 51 95
Private: Grammont, 9 1007 LAUSANNE tel:++41 21 617 03 05
mailto:Philippe(dot)Rochat(at)epfl(dot)ch, http://lbdwww.epfl.ch/~prochat