Re: Structured Types, Oids and Reference Types - Mailing list pgsql-general

 Richard

> Fair enough. Apologies if I made assumptions about your level of knowledge.

That is fine I guess I didn't state my requirements clearly as this is the
first time I have used any of the PostgreSQL lists. I have been using
PostgreSQL for about 2 years. I also forgot to mention that I am emailing
from New Zealand and that when you work I sleep and when I work you sleep, so
that is one reason why I have probably not used the lists before, plus I have
figured out most things that I needed to so far to do with relational
features.

> > Yes I agree but I specifically want to see if lists, arrays, setof or
> > bagof exist in the PostgreSQL environment.
>
> The arrays you see are all there is. Their usage is somewhat limited at the
> moment, afaik you can't check for the existence of a value anywhere within
> an array, only check the nth value.

That solves that problem then.

> No lists, sets or bags I'm afraid. Most of the object-related stuff is the
> older code iirc, there's not been too much development there.

Maybe someone might implement these collection types one day.

> > So going back to table oids. How can you tell what the oid of a table is
> > and how can you refer to it?
>
> select oid from pg_class where relname = 'foo';
>
> But I don't think it's going to help with what you want.

I'll have to make some more tests and then I will let you know.

> > > > 2) Can you dereference tuples or columns in a query by using a
> > > > "deref" function (DEREF is a keyword) for '.' or C type syntax '->'.
> > > > i.e
> > >
> > > You're not thinking in relational terms again.
> >
> > Yes I understand that. I specifically want to look at how to dereference
> > an object using an object relational database.
>
> Nope - barring some feature I've not come across, you're not going to get
> anywhere. I think you're looking for something that's just not in PG.

I guess you are probably right because I have not seemed to be able to get it
to work. However it is like the bug issue in programs, "you can't show that a
program is bug-free, testing only shows the presence of bugs".

> My understanding is that Postgresql's object features come from way back
> when it was still being developed in academia (before the SQL parser even).
> What you *can* do in PG is inherit one table (class) from another, to
> extend person to cover lecturer and student for example.

As part of one of masters projects I am looking at PostgreSQL's object
relational features. Yeah I figured that inheritance issue out, that was
straight forward.

> You could also define your own types for setof etc. - I believe that's how
> some of the specialised geographical stuff was introduced. Probably not
> what you were looking to do I'm afraid.

Yes you are right I just want to see if the collection types: list, bagof,
setof and arrays are already implemented in PostgreSQL.

> What I don't think you'll find is the sort of object-relational stuff to
> tie java/c++ object persistance directly into Postgresql. I'm afraid I
> don't know enough about such stuff to be able to point you to somewhere
> else. Hopefully someone else on the list can.

Okay we will see then.

> I think this list is as good as any. Possibly the interfaces list might be
> useful too, but the developers pop up on general pretty frequently.

I might give interfaces list a go.

> Again apologies for assumptions about your background. I read your message
> thinking you were from a programming background and making your first
> venture into RDBMS land.

That is fine.

Cheers Craig
Email:    craig@mcs.vuw.ac.nz
Web:    http://www.mcs.vuw.ac.nz/~craig