Re: Doubts about FK

On Fri, Sep 12, 2008 at 12:14 PM, Rafael Domiciano
<rafael(dot)domiciano(at)gmail(dot)com> wrote:
> Hi there,
>
> In my DB I have a couple of FK, so the change of referenced columns is a
> quite complicated.
> Today, I DISABLE TRIGGER ALL on the tables envolved and then ENABLE TRIGGER
> ALL to back them.
> Is there a better way to do that?

Depends. Are other people connected to the server when you do it?
disable trigger disables the triggers for everybody, not just you if I
remember correctly. If other folks are using the db, then they can
insert bad data during that period.

> I read something about SET CONSTRAINTS ALL DEFFERED, but I don't know how to
> use it.

the constraints have to created as deferrable to do that. then, in a
transaction, you can do something like:

begin;
update in a way that would normally violate an FK
insert in a way that fixes the previous statement's FK relationship
commit;

and it will work as long as the constraints all make sense by the time
you get to commit.

Note that unique constraints are not deferrable in pgsql.