Re: Any plans on allowing user-defined triggers to

Well, I guess the only moments when you can verify those conditions are
when you insert or delete a project, because it seems logical to me
that, at the moment of a department insertion, you will not have any
projects related to it, so the constraint you need will automatically be
broken.
So, imho, what you can do is to prevent the system to delete a project
when there are only two in a department, or to insert a new one when
there are 8 projects already there.

On Tue, 2004-10-26 at 16:18, Mike Mascari wrote:

> Valentin Militaru wrote:
> > You can do that. But first you have to do some optimisations, like:
> > add a column id(bigserial) to the departamens table, after which you
> > will replace the column department with id_department in the projects
> > table. It is an optimisation, as you are dealing with integer, not text.
>
> Well, that's an argument for surrogate keys, which will invoke a
> philosophical war amongst purists that I won't touch...
>
> > After that, what do you want to achieve? When you are inserting a
> > department, should the server insert 2 to 8 blank records in the
> > projects table which contain the inserted department? Or do you want not
> > to be able to insert a department if there aren't already 2 to 8
> > projects containing that department in the projects table?
>
> I want the database to enforce logical consistency by ensuring that if a
> department exists, there are at a minimum two projects and a maximum of
> eight projects associated with it. Date & Darwen attribute the
> enforcement of such business requirements to database constraints.
> PostgreSQL lacks database constraints, but the result can often be
> achieved through triggers. But I can't figure out how to enforce
> consistency without deferrable triggers and without relying on the
> application to maintain consistency, which is not its job.
>
> Mike Mascari

Valentin Militaru
valentin(dot)militaru(at)telcor(dot)ro
SC Telcor Communications SRL
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