Обсуждение: pl/pgsql, cursors and C function
Hi I'm making my first steps in C functions. I want to avoid doing all the SQL job in them, pl/pgsql looks a better choice. I tried to do this by passing opened cursor from pl/pgsql function to C function. Here is simple C function: #include <server/postgres.h> #include <server/executor/spi.h> PG_FUNCTION_INFO_V1(test2); Datum test2(PG_FUNCTION_ARGS) { Portal p; int n; p=SPI_cursor_find("xxx"); if(!p) elog(ERROR,"Cursor error"); SPI_cursor_fetch(p,true,1); n=SPI_processed; PG_RETURN_INT32(n); } And pl/pgsql one: CREATE OR REPLACE FUNCTION test() returns integer AS ' DECLARE _m CURSOR FOR select id from some_table limit 1; n integer; BEGIN _m=''xxx''; open _m; n=test2(); close _m; return n; END; ' language 'plpgsql'; select test(); I don't understand ERROR message at all: ERROR: SPI_prepare() failed on "SELECT $1 " This error is raised when trying to execute SPI_cursor_fetch. What does it mean? What does the SPI_prepare have to already opened cursor? Where can I find better SPI documentation than "Postgresql Server Programming" ? Regards, Tomasz Myrta
Tomasz Myrta <jasiek@klaster.net> writes: > I don't understand ERROR message at all: > ERROR: SPI_prepare() failed on "SELECT $1 " This is a bug. Or two bugs, actually: one of yours and one of PG's. I have repaired the PG bug with the attached patch. The bug in your code is that your C function needs to call SPI_connect and SPI_finish if it's going to use any SPI operations. regards, tom lane Index: spi.c =================================================================== RCS file: /cvsroot/pgsql-server/src/backend/executor/spi.c,v retrieving revision 1.75.2.3 diff -c -r1.75.2.3 spi.c *** spi.c 14 Feb 2003 21:12:54 -0000 1.75.2.3 --- spi.c 23 Sep 2003 15:09:39 -0000 *************** *** 1387,1393 **** elog(ERROR, "invalid portal in SPI cursor operation"); /* Push the SPI stack */ ! _SPI_begin_call(true); /* Reset the SPI result */ SPI_processed = 0; --- 1387,1394 ---- elog(ERROR, "invalid portal in SPI cursor operation"); /* Push the SPI stack */ ! if (_SPI_begin_call(true) < 0) ! elog(ERROR, "SPI cursor operation called while not connected"); /* Reset the SPI result */ SPI_processed= 0;
>>I don't understand ERROR message at all: >> ERROR: SPI_prepare() failed on "SELECT $1 " > > > > This is a bug. Or two bugs, actually: one of yours and one of PG's. > I have repaired the PG bug with the attached patch. The bug in your > code is that your C function needs to call SPI_connect and SPI_finish > if it's going to use any SPI operations. > > regards, tom lane Thanks a lot. The first answer helped me, the second one - the others. Do you know anything about good source of C functions documentation and examples? Currently I'm walking over .h headers to find some useful functions and macros. Regads, Tomasz Myrta
Tomasz Myrta <jasiek@klaster.net> writes: > Do you know anything about good source of C functions documentation and > examples? Look in the main sources (backend/utils/adt/, mostly) and/or contrib modules for functions that do something like what you need. The only difference between a builtin function and a dynamically loaded one is you have to add the PG_FUNCTION_INFO macro. regards, tom lane