QSqlDriver/handle and subscribeToNotification

[ederbs]

Hi Friends,

I am trying to create an event notifications from the database using PostgreSQL, but I am not understanding how to create this event.

The code connection:

#include <QSqlDatabase>
#include <QSqlDriver>
#include <QVariant>
 
extern "C" {
#include <postgresql/libpq-fe.h>
}
 
inline static bool PQ()
{
        QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
 
        db.setDatabaseName("e193");
        db.setHostName("localhost");
 
        QVariant value = db.driver()->handle();
 
        if (value.typeName() == "PGconn*")
        {
                PGconn *handle = *static_cast<PGconn **>(value.data());
 
                if (handle != 0)
                {}
        }
 
        return true;
}

#include <QSqlDatabase>
#include <QSqlDriver>
#include <QVariant>

extern "C" {
#include <postgresql/libpq-fe.h>
}

inline static bool PQ()
{
        QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");

        db.setDatabaseName("e193");
        db.setHostName("localhost");
 
        QVariant value = db.driver()->handle();

        if (value.typeName() == "PGconn*")
        {
                PGconn *handle = *static_cast<PGconn **>(value.data());

                if (handle != 0)
                {}
        }

        return true;
}

To copy to clipboard, switch view to plain text mode 

With the code above the connection is created without problems, as do more to trigger the event of the database?

When use:

db.driver()->subscribeToNotification("LISTEN notify");

db.driver()->subscribeToNotification("LISTEN notify");

To copy to clipboard, switch view to plain text mode 

Get the following error:

QPSQLDriver::subscribeToNotificationImplementation : database not open.

More connection was opened! Please, someone could help me?

Using Qt SnapShot -> Qt-4.4.0-snapshot-20071205

Thank you, edm.

[mm78]

Why are you getting the handle to the driver? You don't need it to use notifications.

Are you really sure that the connection is open? I can't see any calls to open() in your code. Use isOpen() to see if the connection is really open or not before you call subscribeToNotification(). There are also a few problems in your code: subscribeToNotification() only takes the name of the event, thus you must remove LISTEN; and NOTIFY is a reserved word in PostgreSQL so you can't use it as an event id. My guess is that you want to do something like:

// Already connected to the database somewhere else in your code
QSqlDatabase db = QSqlDatabase::database();
if (db.isOpen())
   db.driver()->subscribeToNotification("someEventId");

// Already connected to the database somewhere else in your code
QSqlDatabase db = QSqlDatabase::database();
if (db.isOpen())
   db.driver()->subscribeToNotification("someEventId");

To copy to clipboard, switch view to plain text mode 

Note that the API is for subscribing to event notifications only. To actually trigger an event notification you'll have to use a query:

QSqlQuery q;
q.exec("NOTIFY someEventId");

QSqlQuery q;
q.exec("NOTIFY someEventId");

To copy to clipboard, switch view to plain text mode 

And to actually get the notification you have to connect to the notification signal.

[ederbs]

Hummm ... Was doing wrong, now with its code above this worked, it was exactly what I wanted.

But I am not able to connect the signal notification "QSqlDriver::notification", I am trying something like this:

QObject::connect(db.driver(), SIGNAL(notification(nAlertTrigger)), this, SLOT(slotRefresh()));

QObject::connect(db.driver(), SIGNAL(notification(nAlertTrigger)), this, SLOT(slotRefresh()));

To copy to clipboard, switch view to plain text mode 

How do I connect the event of notification?

Thanks, edm.

[mm78]

QObject::connect(db.driver(), SIGNAL(notification(const QString&)), this, SLOT(slotRefresh()));

QObject::connect(db.driver(), SIGNAL(notification(const QString&)), this, SLOT(slotRefresh()));

To copy to clipboard, switch view to plain text mode