Re: special integrity constraints

On Mon, 22 Mar 2004, Erik Thiele wrote:

> On Mon, 22 Mar 2004 06:21:28 -0800 (PST)
> Stephan Szabo <sszabo@megazone.bigpanda.com> wrote:
>
> >
> > On Mon, 22 Mar 2004, Erik Thiele wrote:
> >
> > However, foreign keys are implemented using "constraint triggers". They're
> > really not documented much (because they're a not really separately
> > supported implementation detail), but you can theoretically make
> > triggers that are deferred to immediately before commit time.
>
> could you paste some code?
>
>
> create table a (x integer);
>
> create or replace function alwaysfail() returns opaque as '
> begin
>   raise exception ''no no i dont want to'';
> end;
> ' language 'plpgsql';
>
> MAGIC COMMAND INSERT HERE, INSTALL CALL OF alwaysfail() ON
> MODIFICATION OF TABLE a AT COMMIT TIME;

create constraint trigger a_foo1 after insert or update or delete on a
initially deferred for each row execute procedure alwaysfail();

Like I said, it's an implementation detail, so it's not 100% guaranteed to
exist forever, but it's almost certain to last until we have deferrable
non-fk constraints.  It does also obey set constraints so, set constraints
a_foo1 immediate does the checks immediately just as if it were a deferred
constraint.