Re: assertion and company

On Sat, 23 Sep 2006, snake84(at)inwind(dot)it wrote:

> My problem is:

> i have 2 tables,"editoriale" and "ColaboratoreFisso", in the first i
> have the foreign key of the second and in this last table i have an
> attribute named MembroCR that can assume only boolean values...
>
> Now, i have to be sure that every row in "ColaboratoreFisso", that has
> the key also inside "editoriale", has the attribute MembroCR=TRUE.
>
> So i thought to resolve this with an Assertion, but postgresql doesn't
> implement it... in what way i can solve my matter?

You can probably check the condition in a set of after triggers.

I think you'd need an after insert and update trigger on editoriale to
make sure the new value doesn't line up with a MembroCR = false
collaboratoreFisso and I think an after update trigger on
collaboratoreFisso to prevent MembroCR from being set to false on a row
that is referenced.

I think something in the general vein of the following untested, might
work as a starting point. You'll probably need to do some more work on
them.

create or replace function cfe1() returns trigger as $$
begin

perform 1 from CollaboratoreFisso where CollaboratoreFisso.CodiceFiscaleF
= NEW.MembroComitatoRedazione and CollaboratoreFisso.MembroCR = false for
read only;

if found then raise exception '...'; end if;
return NEW;
end;$$
language 'plpgsql';

create trigger cfet1 after insert or update on editoriale for each row
execute procedure cfe1();

create or replace function cfe2() returns trigger as $$
begin
if (NEW.MembroCR = false) then
perform 1 from editoriale where editoriale.MembroComitatoRedazione =
NEW.CodiceFiscaleF for read only;
if found then raise exception '...'; end if;
end if;
return NEW;
end;$$
language 'plpgsql';

create trigger cfet2 after update on CollaboratoreFisso for each row
execute procedure cfe2();

> ANOTHER QUESTION:
>
> I have some problem with my redundancies:
>
> In what way i can implement them? With triggers? I have tried but my
> code doesn't work, i don't know how to use them :(

I'm not sure what you mean by redundancies here.