Strange problem with mysql and QTableView.

[Datakim]

Hi everyone, a newbie at qt requesting a bit of assistance here.

My problem is that I am trying to connect to a mysql database, and then load data from a table into a QTableView. Unfortunately, I have run into some difficulties.

I have done all the necessary mysql bits such as compiling a plugin and such, and I believe I did things correctly since I have managed to create a connection. My problem is that while the code works in one specific circumstance, it does not in another.

My test program is composed of two files, main.cpp and mainwindow.cpp. I am using qtcreator to make this program. I have looked up on how to load data into QTableView and if I do the loading in the main.cpp, it works right. I get a window with the correct data.

However, if I try to do the EXACT same thing with the exact same code from mainwindow.cpp, it fails to work at all. I get no errors or such, the data simply fails to load.

Here is a sample of the code I am using to make a connection that works:

main.cpp:


#include <QtGui/QApplication>
#include "mainwindow.h"

void initializeModel(QSqlTableModel *model)
{
model->setTable("TABLE");
model->setEditStrategy(QSqlTableModel::OnManualSubmit);
model->select();
}


QTableView *createView(const QString &title, QSqlTableModel *model)
{
QTableView *view = new QTableView;
view->setModel(model);
view->setWindowTitle(title);
return view;
}


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


QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setHostName("HOSTNAME");
db.setDatabaseName("DATABASENAME");
db.setUserName("USERNAME");
db.setPassword("PASSWORD");

if (!db.open()) {
qDebug() << db.lastError();
return 1;
}

QSqlTableModel model;

initializeModel(&model);

QTableView *view1 = createView(QObject::tr("Table Model"), &model);
view1->show();

// MainWindow w;
// w.show();


return a.exec();
}


The code above works. However, if I comment the sql code here, and remove the comments that open the MainWindow, and put the same code there, things no longer work.

Mainwindow.cpp


#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QtGui>
#include <QtSql>


MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}

MainWindow::~MainWindow()
{
delete ui;
}

void initializeModel(QSqlTableModel *model)
{
model->setTable("TABLE");
model->setEditStrategy(QSqlTableModel::OnManualSubmit);
model->select();
}

QTableView *createView(const QString &title, QSqlTableModel *model)
{
QTableView *view = new QTableView;
view->setModel(model);
view->setWindowTitle(title);
return view;
}


void MainWindow::on_pushButton_clicked()
{
QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setHostName("HOSTNAME");
db.setDatabaseName("DATABASENAME");
db.setUserName("USERNAME");
db.setPassword("PASSWORD");


if (!db.open()) {
qDebug() << db.lastError();
}

QSqlTableModel model;

initializeModel(&model);

QTableView *view1 = createView(QObject::tr("Table Model"), &model);
view1->show();
}



The code is exactly the same, except it runs from a button click rather than automatically. The information (hostname,databasename,etc are correct).
I have no idea whats wrong. :( Any advice or ideas would be much appreciated.
Thanks

[ChrisW67]

The QSqlTableModel you create at line 49 is on the stack, goes out of scope at the end of that routine, and leaves the view without a model to display. Create it on the heap.

It works in the first example because the model stays in scope long fro the entire lifetime of the view.

[CroOm]

in other words, add the following line to mainwindow.h

QTableView *view1;
QSqlTableModel model;

and assign them in mainwindow.cpp just with the names view1 and model