MySQL connection problem

[myils]

Hi,
I'm using MySQL 5 and Qt 4.3 under Kubuntu 7.04.

I am able to open a connection to the database OK if I do the following:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setDatabaseName("location");
db.setUserName("root");
db.setPassword("blah");
 
if (!db.open()) {
    cerr << "Database did not open successfully!" << endl;
    return false;
}

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setDatabaseName("location");
db.setUserName("root");
db.setPassword("blah");

if (!db.open()) {
    cerr << "Database did not open successfully!" << endl;
    return false;
}

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However when I try and specify a unique connection name like the following, I am unable to connect:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "someConnection");
db.setDatabaseName("location");
db.setUserName("root");
db.setPassword("blah");
 
if (!db.open()) {
    cerr << "Database did not open successfully!" << endl;
    return false;
}

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "someConnection");
db.setDatabaseName("location");
db.setUserName("root");
db.setPassword("blah");

if (!db.open()) {
    cerr << "Database did not open successfully!" << endl;
    return false;
}

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Does anyone know why I am unsuccessful in connecting in the second case?

Additional information:
In the second case the message "Database did not open successfully!" does not print. However when the first query is made the following error messages are received:

QSqlQuery::exec: database not open
Driver not loaded Driver not loaded

A full listing of the erroneous code is shown below:

#include <QApplication>
#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
//#include <QTextStream>
#include <iostream>
#include <QVariant>
using namespace std;
 
static bool createConnection()
{
	QString title;
 
    QSqlQuery query;
	QString sql_string;
 
	sql_string = "SELECT friend FROM friends WHERE username = \"Bob\"";
 
	query.exec(sql_string);
 
	if (!query.isActive())
		std::cerr << qPrintable(query.lastError().text()) << std::endl;
 
 
	while (query.next()) {
		title = query.value(0).toString();
		std::cerr << qPrintable(title) << endl;
	}
 
    return true;
}
 
int main()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "SomeName");
    db.setDatabaseName("location");
	db.setUserName("root");
	db.setPassword("blah");
    if (!db.open()) {
		cerr << "Database did not open successfully!" << endl;
        return false;
    }
 
 
 
    if (!createConnection())
        return 1;
 
	return 0;
}

#include <QApplication>
#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
//#include <QTextStream>
#include <iostream>
#include <QVariant>
using namespace std;

static bool createConnection()
{
	QString title;

    QSqlQuery query;
	QString sql_string;

	sql_string = "SELECT friend FROM friends WHERE username = \"Bob\"";

	query.exec(sql_string);

	if (!query.isActive())
		std::cerr << qPrintable(query.lastError().text()) << std::endl;


	while (query.next()) {
		title = query.value(0).toString();
		std::cerr << qPrintable(title) << endl;
	}

    return true;
}

int main()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "SomeName");
    db.setDatabaseName("location");
	db.setUserName("root");
	db.setPassword("blah");
    if (!db.open()) {
		cerr << "Database did not open successfully!" << endl;
        return false;
    }



    if (!createConnection())
        return 1;

	return 0;
}

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Thanks,
Myils

[wysota]

Check if you have MySQL Qt driver compiled and if you have MySQL client library installed on your system (it's called libmysqlclient).

[myils]

Hi wysota,
I installed Qt4 from the Ubuntu software repository using apt-get. I'm guessing that the MySQL Qt driver is OK since I am able to successfully connect to MySQL provided I do not specify a value for connectionName when calling QSqlDatabase::addDatabase().

I'm also guessing that the MySQL client library is installed on my system since I can find the following files:

/var/lib/dpkg/info/libmysqlclient15off.shlibs
/var/lib/dpkg/info/libmysqlclient15off.list
/var/lib/dpkg/info/libmysqlclient15off.postinst
/var/lib/dpkg/info/libmysqlclient15off.postrm
/var/lib/dpkg/info/libmysqlclient15off.md5sums
/var/lib/dpkg/info/libmysqlclient15-dev.list
/var/lib/dpkg/info/libmysqlclient15-dev.postrm
/usr/lib/libmysqlclient.so.15.0.0
/usr/lib/libmysqlclient_r.so.15.0.0
/usr/lib/libmysqlclient.so.15
/usr/lib/libmysqlclient_r.so.15
/usr/share/doc/libmysqlclient15off
/usr/share/doc/libmysqlclient15off/EXCEPTIONS-CLIENT.gz
/usr/share/doc/libmysqlclient15off/changelog.Debian.gz
/usr/share/doc/libmysqlclient15off/README.Debian
/usr/share/doc/libmysqlclient15off/copyright
/usr/share/doc/libmysqlclient15off/NEWS.Debian.gz

Thanks,
Myils

[wysota]

Maybe the location or user/password are invalid? Can you connect to the database passing the same data using mysql console (mysql -u root -p location)?

[myils]

The "location" table and user/password are valid. I know this because I can connect provided I execute the following:
QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

However I cannot connect to MySQL when I do this:
QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "someConnection");

[wysota]

Your query is surely invalid. You should associate it with the connection you created.

QSqlQuery query(QSqlDatabase::database("SomeName"));
query.exec("...");

QSqlQuery query(QSqlDatabase::database("SomeName"));
query.exec("...");

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[myils]

Thanks wysota,
Your last suggestion has fixed the problem .
Myils