Re: Can I create a TYPE (or DOMAIN) with arguments?

Hello,

I'm trying to create a composite type with an argument, to create one field of this type like character varying(x), but I don't know if this can be done with PostgreSQL. I want something like:
CREATE TYPE mytype AS (
tx character varying(x),
t2nd integer
);
I need to limit the number of chars in this field tx. And different lengths will be used when creating tables with this type (so a Domain will suffer the same problem). I'm not looking for a solution like a separate column with maxChars and a Check, because lots of columns will be required (and others design reasons).

Any suggestions?

Thanks.

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On Jan 9, 2008, at 3:53 AM, R.A. wrote:

> Hello,
>
> I'm trying to create a composite type with an argument, to create
> one field of this type like character varying(x), but I don't know
> if this can be done with PostgreSQL. I want something like:
> CREATE TYPE mytype AS (
> tx character varying(x),
> t2nd integer
> );
> I need to limit the number of chars in this field tx. And different
> lengths will be used when creating tables with this type (so a
> Domain will suffer the same problem). I'm not looking for a
> solution like a separate column with maxChars and a Check, because
> lots of columns will be required (and others design reasons).

Postgres doesn't support parameterized type declarations directly
(that I've ever heard of), but you could probably write a function
that uses EXECUTE to do this.

Erik Jones

DBA | Emma®
erik(at)myemma(dot)com
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On Jan 9, 2008 4:53 AM, R.A. <adeveloper(at)bluebottle(dot)com> wrote:
> Hello,
>
> I'm trying to create a composite type with an argument, to create one field of this type like character varying(x), but I don't know if this can be done with PostgreSQL. I want something like:
> CREATE TYPE mytype AS (
> tx character varying(x),
> t2nd integer
> );
> I need to limit the number of chars in this field tx. And different lengths will be used when creating tables with this type (so a Domain will suffer the same problem). I'm not looking for a solution like a separate column with maxChars and a Check, because lots of columns will be required (and others design reasons).

It would be really neat if you could do that, but you can't :-(. What
you can do is make a trigger function taking mytype which and apply
the constraint that way...

merlin

On Thu, Jan 10, 2008 at 08:58:07AM -0600, Erik Jones wrote:
> Postgres doesn't support parameterized type declarations directly
> (that I've ever heard of), but you could probably write a function
> that uses EXECUTE to do this.

IIRC 8.3 will include the user-defined typmod which will allow such
constructs...

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Those who make peaceful revolution impossible will make violent revolution inevitable.
> -- John F Kennedy

Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> On Thu, Jan 10, 2008 at 08:58:07AM -0600, Erik Jones wrote:
>> Postgres doesn't support parameterized type declarations directly
>> (that I've ever heard of), but you could probably write a function
>> that uses EXECUTE to do this.

> IIRC 8.3 will include the user-defined typmod which will allow such
> constructs...

That won't help for this particular problem, though --- composite types
don't take typmods, and there'd be no mechanism to pass it down to the
varchar field if they did. I don't think the OP can solve his problem
just with spare parts. In 8.3 he could write a primitive type that
behaves the way he wants, but it'd take an annoyingly large amount
of custom C code :-(

regards, tom lane

I think the function-trigger approach will be useful to me to bypass this problem.

Thanks to all again for your suggestions!

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