Re: Get TupleDesc for extension-defined types

On Wed, Sep 18, 2024 at 1:09 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

> Hi
>
> st 18. 9. 2024 v 9:04 odesílatel Florents Tselai <
> florents(dot)tselai(at)gmail(dot)com> napsal:
>
>> Correct me if I'm wrong,
>> but for an extension that defines composite types,
>> there's currently no easy way to get a TupleDesc, even for its own types.
>>
>> Something like
>> TupleDesc get_extension_type_tupledesc(const char *extname, const char
>> *typname)
>>
>> Here's a routine I've stolen borrowed from pramsey's code and have been
>> using ever since.
>>
>> Could this be exposed in extension.h ? (probably without the version
>> check)
>>
>
> I don't think this functionality is generally useful. Wrapping
> TypeGetTupleDesc(typoid, NIL) is very specific, and probably this code
> should be inside the extension.
>
> Different question is API for searching in system catalog and
> dependencies. I can imagine some functions like
>

That's a better phrasing

>
> Oid extid = get_extension_id(extname);
> Oid objid = get_extension_object_id(extid, schema_can_be_null, name,
> TYPEOID); // can be used for routine, table, ...
>
> tupdesc = TypeGetTupleDesc(objid, NIL);
>

These are valid.
For context:
The "problem" (inconvenience really) I'm trying to solve is this:
Most extensions define some convenient PG_GETARG_MYTYPE(n) macros.
When these types are varlena, things are easy.

When they're composite types though things get more verbose.
i.e. the lines of code the author needs to get from a Datum argument to
struct MyType are too many
and multiple extensions copy-paste the same logic.

My hope is we could come up with a few routines that ease and standardize
this a bit.

You're right that extname isn't unique, so Oid should be the argument for
extension, rather than char *extname,
but in my mind the "default" is "the current extension" , but no arguing
about that.

>
> Regards
>
> Pavel
>
>
>