QSqlDatabase usage

[goes2bob]

I have an application that is using an SQLite database. I am trying to follow Qt examples by connecting via the conneciton.h file, but do not seem to get it.
I have main.cpp call gui.cpp which creates a stackedWidget with 4 widgets, 2 of these will (may) someday include QTableViews that are simple read-only tables from a database. I have seperated the 4 different widgets into their own classes (which are also in different files - not sure if that is important or not). I am trying to have one of the widget classes query the db and the query returns false.
Where should I actually put the "createConnection()" call (it's in main.cpp right now), and how do I get a pointer (or something else) to use that my query can use. I think I am thinking too much - cannot see thru the fog .
-Thanks in advance
Goes2bob

[ashukla]

Where should I actually put the "createConnection()" call (it's in main.cpp right now), and how do I get a pointer (or something else) to use that my query can use. I think I am thinking too much - cannot see thru the fog

main.cpp is a right place to call createConnection. You can use like this;

#include <QApplication>
#include "connection.h"
 
 
int main(int argc, char ** argv)
{
	QApplication app( argc, argv );
	if(!createConnection())
		return app.exec();
	......
	......
	......
 
	return app.exec();
}

#include <QApplication>
#include "connection.h"


int main(int argc, char ** argv)
{
	QApplication app( argc, argv );
	if(!createConnection())
		return app.exec();
	......
	......
	......
	
	return app.exec();
}

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[gboelter]

I have main.cpp call gui.cpp which creates a stackedWidget with 4 widgets, 2 of these will (may) someday include QTableViews that are simple read-only tables from a database.

I'm a beginner too, so may be I am not right, but my main.cpp looks only like this:

// main.cpp
#include <QApplication>
 
int main( int argc, char* argv[])
{
    QApplication app(argc, argv);
 
    Erpel myErpel;
    myErpel.show();
 
    return app.exec();
}

// main.cpp
#include <QApplication>

int main( int argc, char* argv[])
{
    QApplication app(argc, argv);

    Erpel myErpel;
    myErpel.show();

    return app.exec();
}

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Then I have a file called Erpel.cpp. This is the file where I put the "createConnection()" call.

// Erpel.cpp
#include "Erpel.h"
 
Erpel::Erpel(QWidget *parent) : QMainWindow( parent )
{
    setupUi(this);
 
    stackedWidget -> setCurrentIndex(0);
 
    connect( actionHome,SIGNAL (triggered()), this, SLOT(slotHome()) );
    connect( actionBackup,SIGNAL (triggered()), this, SLOT(fileBackup()) );
    connect( actionRestore,SIGNAL (triggered()), this, SLOT(fileRestore()) );
 
    // more code follows here ....
}
 
bool Erpel::dbConnect(QString dbName)
{
    QString curDir = QCoreApplication::applicationDirPath();
    QString iniFile = curDir+"/erpel.ini";             // get some parameters from erpel.ini
    QSettings settings(iniFile, QSettings::IniFormat);
 
    QString dbdriver = settings.value("database/dbdriver").toString();
    QString dbhost   = settings.value("database/dbhost").toString();
    QString dbname   = settings.value("database/dbname").toString();
    QString dbuser   = settings.value("database/dbuser").toString();
    QString dbpasswd = settings.value("database/dbpasswd").toString();
 
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
 
    db.setHostName(dbhost);
    db.setDatabaseName(dbName);
    db.setUserName(dbuser);
    db.setPassword(dbpasswd);
 
    bool connect2Db = db.open();        // try to open the database ...
 
    if (!connect2Db)
    {
        QMessageBox::critical(0, qApp->tr("ERROR!"),
                              qApp->trUtf8("I was not able to connect to your database!"),
                              QMessageBox::Cancel);
        return false;
    }
 
    qDebug() << "dbconnect" << db.isValid();
 
    return true;
}

// Erpel.cpp
#include "Erpel.h"

Erpel::Erpel(QWidget *parent) : QMainWindow( parent )
{
    setupUi(this);

    stackedWidget -> setCurrentIndex(0);

    connect( actionHome,SIGNAL (triggered()), this, SLOT(slotHome()) );
    connect( actionBackup,SIGNAL (triggered()), this, SLOT(fileBackup()) );
    connect( actionRestore,SIGNAL (triggered()), this, SLOT(fileRestore()) );

    // more code follows here ....
}

bool Erpel::dbConnect(QString dbName)
{
    QString curDir = QCoreApplication::applicationDirPath();
    QString iniFile = curDir+"/erpel.ini";             // get some parameters from erpel.ini
    QSettings settings(iniFile, QSettings::IniFormat);

    QString dbdriver = settings.value("database/dbdriver").toString();
    QString dbhost   = settings.value("database/dbhost").toString();
    QString dbname   = settings.value("database/dbname").toString();
    QString dbuser   = settings.value("database/dbuser").toString();
    QString dbpasswd = settings.value("database/dbpasswd").toString();

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

    db.setHostName(dbhost);
    db.setDatabaseName(dbName);
    db.setUserName(dbuser);
    db.setPassword(dbpasswd);

    bool connect2Db = db.open();        // try to open the database ...

    if (!connect2Db)
    {
        QMessageBox::critical(0, qApp->tr("ERROR!"),
                              qApp->trUtf8("I was not able to connect to your database!"),
                              QMessageBox::Cancel);
        return false;
    }

    qDebug() << "dbconnect" << db.isValid();

    return true;
}

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and

// Erpel.h                      // not complete, only as a sample ....
#ifndef ERPEL_H
#define ERPEL_H
 
#include <QtGui>
#include <QtCore/QVariant>
#include <QSettings>
 
#include <QtSql/QSqlDatabase>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQuery>
#include <QtSql/QSqlRecord>
 
#include <QDebug>
 
#include "ui_erpel.h"
 
class Erpel : public QMainWindow, public Ui::Erpel
{
    Q_OBJECT
 
public:
    Erpel (QWidget * parent = 0);
    ~Erpel();
 
    QString dbdriver;
    QString dbhost;
    QString dbname;
    QString dbuser;
    QString dbpasswd;
 
    bool dbConnect(QString dbName);
 
public slots:
    void slotClose();
 
private:
    void adjustHeader();
 
private slots:
 
    void editButton(int name);
 
protected:
 
signals:
 
};
#endif //ERPEL_H

// Erpel.h                      // not complete, only as a sample ....
#ifndef ERPEL_H
#define ERPEL_H

#include <QtGui>
#include <QtCore/QVariant>
#include <QSettings>

#include <QtSql/QSqlDatabase>
#include <QtSql/QSqlError>
#include <QtSql/QSqlQuery>
#include <QtSql/QSqlRecord>

#include <QDebug>

#include "ui_erpel.h"

class Erpel : public QMainWindow, public Ui::Erpel
{
    Q_OBJECT

public:
    Erpel (QWidget * parent = 0);
    ~Erpel();

    QString dbdriver;
    QString dbhost;
    QString dbname;
    QString dbuser;
    QString dbpasswd;

    bool dbConnect(QString dbName);

public slots:
    void slotClose();

private:
    void adjustHeader();

private slots:

    void editButton(int name);

protected:

signals:

};
#endif //ERPEL_H

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I think I am thinking too much - cannot see thru the fog .

I know that feeling very well, but may be the code above will help you a little bit to find your way even when it's foggy ....

[jpn]

Perhaps you forgot to call Erpel::dbConnect()?

[gboelter]

Perhaps you forgot to call Erpel::dbConnect()?

Hello jpn,

I prefer to call Erpel::dbConnect() when I need some datas from my database, not during starting the program.

Like this for example:

void Erpel::showKasseLayout()
{
    if (dbConnect(currentMandant))
    {
        QSqlQuery query;
        QString image;
 
        query.prepare("SELECT ID, Beschriftung, ArtikelNummer, Image, ToolTip, TimeStamp FROM kassenlayout");
 
        query.exec();
 
        if (query.isSelect())
            query.first();
 
       // more code follows here ....

void Erpel::showKasseLayout()
{
    if (dbConnect(currentMandant))
    {
        QSqlQuery query;
        QString image;

        query.prepare("SELECT ID, Beschriftung, ArtikelNummer, Image, ToolTip, TimeStamp FROM kassenlayout");

        query.exec();

        if (query.isSelect())
            query.first();

       // more code follows here ....

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I think it's a little bit more code and a little bit more to do for the computer, but it's safer.

Is that correct?