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Date: Tue, 06 Jul 2010 13:00:33 -0700
From: Joe Conway <mail@joeconway.com>
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On 07/06/2010 12:42 PM, Eliot Gable wrote:
> Thanks for suggesting array_unnest(). I think that will actually prove
> more useful to me than the other example I'm using for extracting my
> data from an array. I was actually planning on computing the order on
> the first call and storing it in a linked list which gets returned one
> item at a time until all rows have been returned. Also, I found a code
> example using Google that showed someone storing data across function
> calls using that pointer. I used their example to produce this:
>=20
> <snip>
>     if(SRF_IS_FIRSTCALL()) {
>         funcctx =3D SRF_FIRSTCALL_INIT();
>=20
>         /* This is where we stick or sorted data for returning later */=

>         funcctx->user_fctx =3D
> MemoryContextAlloc(funcctx->multi_call_memory_ctx, sizeof(sort_data));
>         oldcontext =3D MemoryContextSwitchTo(funcctx->multi_call_memory=
_ctx);
>         data =3D (sort_data*) funcctx->user_fctx;
> </snip>
>=20
> I have a structure set up that is typedef'd to "sort_data" which stores=

> pointers to various things that I need to survive across the calls.
> Since this seems to be what you are suggesting, I assume this is the
> correct approach.

This approach works, but you could also use the SFRM_Materialize mode
and calculate the entire result set in one go. That tends to be simpler.
See, for example crosstab_hash() in contrib/tablefunc for an example.

FWIW, there are also some good examples of array handling in PL/R, e.g.
pg_array_get_r() in pg_conversion.c

HTH,

Joe

--=20
Joe Conway
credativ LLC: http://www.credativ.us
Linux, PostgreSQL, and general Open Source
Training, Service, Consulting, & Support


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