Re: Fwd: Re: Referencing

lucas(at)presserv(dot)org wrote:
> Quoting Daryl Richter <daryl(at)brandywine(dot)com>:
>
>> lucas(at)presserv(dot)org wrote:
>> > Quoting Daryl Richter <daryl(at)brandywine(dot)com>:
>> >> It's hard to say without knowing more precisely what you are trying to
>> >> model, but I think this push you in the right direction:
>> >>
>> > Okay, but references between (output/input) and ACTIVITY tables is 1
>> to N.
>> > OUTPUT/INPUT - 1
>> > to
>> > ACTIVITY - N.
>> > And not N to 1 how the example.
>> > Then the reference field need to be on "ACTIVITY (send/buy)" table.
>> >
>>
>> Ahh, ok. In that case I reverse it like so:
>>
>> -- This table hold everything in common for inputs/outputs
>> create table transfer(
>> id serial primary key
>> );
>
>
> Yes, I think it was what I wanted.
> And how I check if a register in "Transfer" table is only referenciable
> by ONE
> table (OR "output" OR "input")?? Would I create a Trigger like:
> CREATE or REPLACE FUNCTION TG_output_check() RETURNS TRIGGER AS
> $$
> BEGIN
> IF exists (select 1 from input where transfer_id=NEW.transfer_id) THEN
> Raise Exception 'This activity (transfer) is alread setted to INPUT';
> END IF;
> RETURN NEW;
> END;
> $$ language 'plpgsql'; CREATE TRIGGER TG_output_check BEFORE INSERT or
> UPDATE
> on OUTPUT EXECUTE PROCEDURE TG_output_check();
> CREATE or REP...--- and the some function to INPUT ---
>
> Or is there another way to check it?
>
> Thank you again.
>

Exactly, except for the small change that your trigger declaration needs
"for each row" as shown below:

CREATE TRIGGER TG_output_check BEFORE INSERT or UPDATE on output
for each row EXECUTE PROCEDURE TG_output_check();

--
Daryl