From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
---|---|
To: | Erik Thiele <erik(at)thiele-hydraulik(dot)de> |
Cc: | achill(at)matrix(dot)gatewaynet(dot)com, pgsql-sql(at)postgresql(dot)org |
Subject: | Re: special integrity constraints |
Date: | 2004-03-22 16:34:54 |
Message-ID: | 20040322083110.X58785@megazone.bigpanda.com |
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Lists: | pgsql-docs pgsql-sql |
On Mon, 22 Mar 2004, Erik Thiele wrote:
> On Mon, 22 Mar 2004 06:21:28 -0800 (PST)
> Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)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.
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