I have a form with 2 PuchButtons and a TableView created using QTCreator. Now I want to populate TableView with data from SQL database using QSqlTableModel.
My question is: Why when i allocate QSqlTableModel in PushButton1Click everything is ok, and when I allacate it in MainWindow constructor the data from database doesn't show on TableView.
(First I click button 1 to open database, then I click button 2 to fetch data)
Here is declaration of mainwindow class:
Qt Code: 
  1. class MainWindow : public QMainWindow
  2. {
  3.     Q_OBJECT
  4.  
  5. public:
  6.     MainWindow(QWidget *parent = 0);
  7.     ~MainWindow();
  8.  
  9. private:
  10.     Ui::MainWindow *ui;
  12.  
  13. private slots:
  14.     bool PushButton1Click();
  15.     bool PushButton2Click();
  16.  
  17. };
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Here is code which works:
Qt Code: 
  1. #include "mainwindow.h"
  2. #include "ui_mainwindow.h"
  3.  
  4. MainWindow::MainWindow(QWidget *parent)
  5.     : QMainWindow(parent), ui(new Ui::MainWindow)
  6. {
  7.      ui->setupUi(this);
  8.      // m = new QSqlTableModel(this);       // NOT OK !!!!!!!!
  9. }
  10.  
  11.  
  12. MainWindow::~MainWindow()
  13. {
  14.     delete ui;
  15. }
  16.  
  17.  
  18. bool MainWindow::PushButton1Click()
  19.   {
  20.   QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
  21.   db.setHostName("localhost");
  22.   db.setDatabaseName("axis");
  23.   db.setUserName("root");
  24.   db.setPassword("kosa1980");
  25.   bool ret = db.open();
  26.  
  27.   m = new QSqlTableModel(this);         // OK !!!!!!!!
  28.   return ret;
  29.   }
  30.  
  31. bool MainWindow::PushButton2Click()
  32. {
  33.      m->setTable("wagi");
  34.      m->setEditStrategy(QSqlTableModel::OnManualSubmit);
  35.      m->select();
  36.      m->removeColumn(0);
  37.      m->setHeaderData(0, Qt::Horizontal, QObject::tr("numer_seryjny"));
  38.      m->setHeaderData(1, Qt::Horizontal, QObject::tr("typ"));
  39.  
  40.      ui->tableView->setModel(m);
  41.  
  42.      return true;
  43. }
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Here is code which doesn't work:
Qt Code: 
  1. #include "mainwindow.h"
  2. #include "ui_mainwindow.h"
  3.  
  4. MainWindow::MainWindow(QWidget *parent)
  5.     : QMainWindow(parent), ui(new Ui::MainWindow)
  6. {
  7.      ui->setupUi(this);
  8.      m = new QSqlTableModel(this);       // NOT OK !!!!!!!!
  9. }
  10.  
  11. MainWindow::~MainWindow()
  12. {
  13.     delete ui;
  14. }
  15.  
  16. bool MainWindow::PushButton1Click()
  17.   {
  18.   QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
  19.   db.setHostName("localhost");
  20.   db.setDatabaseName("axis");
  21.   db.setUserName("root");
  22.   db.setPassword("kosa1980");
  23.   bool ret = db.open();
  24.  
  25.   //m = new QSqlTableModel(this);         // OK !!!!!!!!
  26.   return ret;
  27.   }
  28.  
  29. bool MainWindow::PushButton2Click()
  30. {
  31.      m->setTable("wagi");
  32.      m->setEditStrategy(QSqlTableModel::OnManualSubmit);
  33.      m->select();
  34.      m->removeColumn(0);
  35.      m->setHeaderData(0, Qt::Horizontal, QObject::tr("numer_seryjny"));
  36.      m->setHeaderData(1, Qt::Horizontal, QObject::tr("typ"));
  37.  
  38.      ui->tableView->setModel(m);         
  39.  
  40.      return true;
  41. }
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Why second version doesn't work?