From: Szymon Drejewicz <drejewic@...>
Date: 2003-02-12T17:22:16+09:00
Subject: PostgreSQL and embedded Ruby

Hello,

INTRO: I would like to build simple application in C to deal with 
PostgreSQL, but part of work should be done by RUBY.

PROBLEM: I don't want to make new connection with PGSQL in Ruby script 
but attach existing one ('conn' variable as below) from C.

QUESTION: Is it possible to attach to Postgres connection from C in Ruby 
script? And how to do it?

Szymon Drejewicz

#=======================================================================
#include <stdlib.h>
#include <libpq-fe.h>
#include <ruby.h>
#include "postgres.c"

int main(int argc, char** argv) {
   PGresult *result;
   PGconn *conn;
   int nFields;
   int i;
   int j;
   conn = PQconnectdb("");

   if(PQstatus(conn) == CONNECTION_OK) {
     printf("connection made\n");
     result = PQexec(conn, "SELECT COUNT(*) FROM studenci");

     printf("Wy�wietlam wynik za pomoc� C:\n");
     /* first, print out the attribute names */
     nFields = PQnfields(result);
     for (i = 0; i < nFields; i++)
       printf("%-15s", PQfname(result, i));
     printf("\n\n");
     /* next, print out the rows */
     for (i = 0; i < PQntuples(result); i++) {
       for (j = 0; j < nFields; j++)
	printf("%-15s", PQgetvalue(result, i, j));
       printf("\n");
     }

     printf("Teraz spr�buj� przekaza� wynik SELECTA do skryptu Ruby'ego, 
kt�ry wy�wietli to samo co powy�ej:");
     ruby_init();
     ruby_options(argc,argv);
     /* Udost�pniam Ruby'emu po��czenie z PostgreSQL'em  */
     ruby_init_loadpath();
     rb_require("postgres");
     //-----------------PROBLEM BEGIN
     VALUE DBconn = Data_Wrap_Struct(rb_cPGconn, 0, free_pgconn, conn);
     //    rb_obj_call_init(DBconn,0,0);
     VALUE connection = conn;
     rb_define_variable("$conn",&connection);
     rb_eval_string("puts '\nTEST\n'");
     rb_eval_string("a = $conn.query('select count(*) from 
studenci')[0][0] \n puts a");
     //-----------------PROBLEM END
   }
   else
     printf("connection failed: %s\n", PQerrorMessage(conn));

   PQfinish(conn);
   return EXIT_SUCCESS;
}