Thread: interperting type oid in C code

I'm working on a foreign data wrapper and I want to switch based on the column type.  Specifically, if the column type in the external table is the same as in the (locally defined) foreign table then I can get some speedup for some types.

Through the ForeignScanState object I can get TupleDesc and AttInMetadata opjects, and through there I can get the Oid of the column type, but now I'm stumped.  How can I programmatically check whether Oid X refers to type int4, or whatever?

Thanks.

SELECT typname
   FROM pg_type
 WHERE oid = Oid_x;

On Mon, Oct 19, 2015 at 2:36 PM, Ken Been <kbbeen@gmail.com> wrote:

I'm working on a foreign data wrapper and I want to switch based on the column type.  Specifically, if the column type in the external table is the same as in the (locally defined) foreign table then I can get some speedup for some types.

Through the ForeignScanState object I can get TupleDesc and AttInMetadata opjects, and through there I can get the Oid of the column type, but now I'm stumped.  How can I programmatically check whether Oid X refers to type int4, or whatever?

Thanks.

--

Melvin Davidson
I reserve the right to fantasize.  Whether or not you
wish to share my fantasy is entirely up to you.

Ken Been wrote:
> Thanks, but I actually wanted to do it from C code.  But anyway I think I
> found the answer: use the symbolic constants in catalog/pg_type.h, such as
> INT4OID.

You can probably use
SearchSysCache1(TYPEOID, ObjectIdGetDatum(your_oid))
or perhaps
lookup_type_cache(your_oid).

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Ken Been wrote:
> Those are more complicated, and it's not obvious to me how to use them.  I
> really think that all I need is something as simple as "if (my_oid ==
> INT4OID) {...}".  Is there any reason why I shouldn't just do that?

I don't know.  I was thinking that you might want to handle a larger set
of type OIDs.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services