Thread: Re: Get TupleDesc for extension-defined types

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)

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

Hi

st 18. 9. 2024 v 9:04 odesílatel Florents Tselai <florents.tselai@gmail.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