Re: C function to return tuple

I have these types:
CREATE TYPE p_type AS
(

x double precision,
y double precision

);
CREATE TYPE d_type AS
(

i p_type,
e p_type,
id integer

);

CREATE OR REPLACE FUNCTION d_swap(d_type)
RETURNS d_type
AS '/home/user/PostgreSQL/9.0/lib/mylib','d_swap'
LANGUAGE C STRICT;

My problem is that I don't know how to construct the d_type tuple in the c
function. I read the documentation but it only explains how i could do that
for a more simple type like p_type.
The difficulty is that d_type has attributes of p_type.
Thank you in advance.

This is the c code I wrote until now:
Datum d_swap(PG_FUNCTION_ARGS) {
HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);
HeapTupleHeader i;
HeapTupleHeader e;
bool isnull;

TupleDesc tupdesc;
Datum values[3];
HeapTuple tuple;
int tuplen;
bool *nulls;

i = DatumGetHeapTupleHeader(GetAttributeByName(t, "i", &isnull));
e = DatumGetHeapTupleHeader(GetAttributeByName(t, "e", &isnull));

if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("function returning record called in context that cannot accept type
record")));
}

BlessTupleDesc(tupdesc);

values[0] = e;
values[1] = i;
values[2] = GetAttributeByName(t, "id", &isnull);

tuplen = tupdesc->natts;
nulls = palloc(tuplen * sizeof (bool));

tuple = heap_form_tuple(tupdesc, values, nulls);

pfree(nulls);

PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
}

Marios Vodas <mvodas(at)gmail(dot)com> writes:
> My problem is that I don't know how to construct the d_type tuple in the c
> function.

Seems like the main problem with that function is that you're passing
an uninitialized "nulls" array to heap_form_tuple.

I kinda wonder why you are using a fixed-length values array together
with a variable-length, dynamically allocated nulls array, but that'
just odd style not wrong in itself.

regards, tom lane

I see what you mean and I changed the code BUT still my main problem is that
I want to know how to fill values array. I remind you that d_type contains
attributes of another composite type p_type.
I need a solution to that because I need to use it in other parts of the
code.

Datum d_swap(PG_FUNCTION_ARGS) {
HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);
HeapTupleHeader i;
HeapTupleHeader e;
bool isnull;

TupleDesc tupdesc;
Datum values[3];
HeapTuple tuple;

i = DatumGetHeapTupleHeader(GetAttributeByName(t, "i", &isnull));
e = DatumGetHeapTupleHeader(GetAttributeByName(t, "e", &isnull));

if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("function returning record called in context that cannot accept type
record")));
}

BlessTupleDesc(tupdesc);

//I need to get this working
*values[0] = e;*
* values[1] = i;*
* values[2] = GetAttributeByName(t, "id", &isnull);*

tuple = heap_form_tuple(tupdesc, values, &isnull);

PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
}

On Sun, Sep 26, 2010 at 7:16 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Marios Vodas <mvodas(at)gmail(dot)com> writes:
> > My problem is that I don't know how to construct the d_type tuple in the
> c
> > function.
>
> Seems like the main problem with that function is that you're passing
> an uninitialized "nulls" array to heap_form_tuple.
>
> I kinda wonder why you are using a fixed-length values array together
> with a variable-length, dynamically allocated nulls array, but that'
> just odd style not wrong in itself.
>
> regards, tom lane
>

Marios Vodas <mvodas(at)gmail(dot)com> writes:
> //I need to get this working
> *values[0] = e;*
> * values[1] = i;*

Maybe you're missing HeapTupleGetDatum() there? Just from a data type
cleanliness standpoint, you shouldn't ever assign something to Datum or
vice versa without applying the correct conversion macro.

regards, tom lane

Suppose I had the data that form the returning tuple in 5 variables like
this:
float8 xi = 1;
float8 yi = 2;
float8 xe = 3;
float8 ye = 4;
int32 id = 1;

In addition the function wouldn't have any input parameters. It just returns
a tuple of type d_type.
Can you tell me how it is possible to form the tuple? My problem here is
that I DON'T have HeapTupleHeaders i and e already formed (those two are of
p_type) so I have to form them somehow.

On Sun, Sep 26, 2010 at 7:52 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Marios Vodas <mvodas(at)gmail(dot)com> writes:
> > //I need to get this working
> > *values[0] = e;*
> > * values[1] = i;*
>
> Maybe you're missing HeapTupleGetDatum() there? Just from a data type
> cleanliness standpoint, you shouldn't ever assign something to Datum or
> vice versa without applying the correct conversion macro.
>
> regards, tom lane
>

Do you think it would be better to change d_type to this?
CREATE TYPE d_type AS
(

xi double precision,
yi double precision,
xe double precision,
ye double precision,
id integer

);
*Note: This is NOT something I want to do but if there is no other way to
form d_type tuple from the variables...*

On Sun, Sep 26, 2010 at 8:29 PM, Marios Vodas <mvodas(at)gmail(dot)com> wrote:

> Suppose I had the data that form the returning tuple in 5 variables like
> this:
> float8 xi = 1;
> float8 yi = 2;
> float8 xe = 3;
> float8 ye = 4;
> int32 id = 1;
>
> In addition the function wouldn't have any input parameters. It just
> returns a tuple of type d_type.
> Can you tell me how it is possible to form the tuple? My problem here is
> that I DON'T have HeapTupleHeaders i and e already formed (those two are
> of p_type) so I have to form them somehow.
>