[ShopSuite-dev] asynchronous notification + trigger

[Davi Leal]

I am trying to add n-tier support, that is to say, automatic GUI
updating from the Data Base state change: insert, delete, update.

I have checked the attached example (2-tier) and it works. I will check
it with two clients (n-tier). Maybe this next weekend.

Reference: Install debian postgresql-doc >= 7.1.3
- /usr/share/doc/postgresql-doc/html/libpq-example.html   (See attached
file)
  Example 1-2. libpq Example Program 2

  Follow the steps showed inside the testlibpq2.c file:
  * testlibpq2.c
  *  Test of the asynchronous notification interface
  *
  * Start this program, then from psql in another window do
  *   NOTIFY TBL2;
  *
  * Or, if you want to get fancy, try this:
  * Populate a database with the following:
  *
  *   CREATE TABLE TBL1 (i int4);
  *
  *   CREATE TABLE TBL2 (i int4);
  *
  *   CREATE RULE r1 AS ON INSERT TO TBL1 DO
  *     (INSERT INTO TBL2 values (new.i); NOTIFY TBL2);
  *
  * and do
  *
  *   INSERT INTO TBL1 values (10);


Additional references:
- /usr/share/doc/postgresql-doc/html/plpgsql-trigger.html
- /usr/share/doc/postgresql-doc/html/trigger-examples.html


Davi

/*
 * testlibpq2.c
 *  Test of the asynchronous notification interface
 *
 * Start this program, then from psql in another window do
 *   NOTIFY TBL2;
 *
 * Or, if you want to get fancy, try this:
 * Populate a database with the following:
 *
 *   CREATE TABLE TBL1 (i int4);
 *
 *   CREATE TABLE TBL2 (i int4);
 *
 *   CREATE RULE r1 AS ON INSERT TO TBL1 DO
 *     (INSERT INTO TBL2 values (new.i); NOTIFY TBL2);
 *
 * and do
 *
 *   INSERT INTO TBL1 values (10);
 *
 */
#include <stdio.h>
#include "libpq-fe.h"

void
exit_nicely(PGconn *conn)
{
    PQfinish(conn);
    exit(1);
}

main()
{
    char       *pghost,
               *pgport,
               *pgoptions,
               *pgtty;
    char       *dbName;
    int         nFields;
    int         i,
                j;

    PGconn     *conn;
    PGresult   *res;
    PGnotify   *notify;

    /*
     * begin, by setting the parameters for a backend connection if the
     * parameters are null, then the system will try to use reasonable
     * defaults by looking up environment variables or, failing that,
     * using hardwired constants
     */
    pghost = NULL;              /* host name of the backend server */
    pgport = NULL;              /* port of the backend server */
    pgoptions = NULL;           /* special options to start up the backend
                                 * server */
    pgtty = NULL;               /* debugging tty for the backend server */
    dbName = getenv("USER");    /* change this to the name of your test
                                 * database */

    /* make a connection to the database */
    conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

    /*
     * check to see that the backend connection was successfully made
     */
    if (PQstatus(conn) == CONNECTION_BAD)
    {
        fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
        fprintf(stderr, "%s", PQerrorMessage(conn));
        exit_nicely(conn);
    }

    res = PQexec(conn, "LISTEN TBL2");
    if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "LISTEN command failed\n");
        PQclear(res);
        exit_nicely(conn);
    }

    /*
     * should PQclear PGresult whenever it is no longer needed to avoid
     * memory leaks
     */
    PQclear(res);

    while (1)
    {

        /*
         * wait a little bit between checks; waiting with select()
         * would be more efficient.
         */
        sleep(1);
        /* collect any asynchronous backend messages */
        PQconsumeInput(conn);
        /* check for asynchronous notify messages */
        while ((notify = PQnotifies(conn)) != NULL)
        {
            fprintf(stderr,
                 "ASYNC NOTIFY of '%s' from backend pid '%d' received\n",
                    notify->relname, notify->be_pid);
            free(notify);
        }
    }

    /* close the connection to the database and cleanup */
    PQfinish(conn);

    return 0;
}