Database and QSqlRelationalTableModel problem

[MarkoSan]

Why does the following code:

CBrowserWindow::CBrowserWindow(QWidget *parent, CDatabaseFoundation* pDatabase, QString sTableName, QString windowCaption)
 : QDialog(parent)
{
  m_pModel=new QSqlRelationalTableModel(parent);  // creates new model
  Q_CHECK_PTR(m_pModel);  // checks for succesful creation
  m_pModel->setTable(sTableName); // sets table name
 
  m_pColumnNames=new QStringList(); // creates new string list
  Q_CHECK_PTR(m_pColumnNames);  // checks for succesful creation
 
  // fetches record
  m_pTableRecord=new QSqlRecord(); // creates new record
  Q_CHECK_PTR(m_pTableRecord);  // checks for susccesful creation
  m_pTableRecord=&pDatabase->m_Database.record(sTableName); // fetches column names
  QSqlRecord tempRec=pDatabase->m_Database.record(sTableName); // fetches column names
  m_pTableRecord=new QSqlRecord(tempRec); // read column names
  Q_CHECK_PTR(m_pTableRecord);
 
  if (!m_pTableRecord->isEmpty()) {
    for (m_iIndex=0; m_iIndex<m_pTableRecord->count(); m_iIndex++) {
      m_pColumnNames->append(m_pTableRecord->fieldName(m_iIndex));
    }
  } // if
 
  createBrowserContens(this, pDatabase, m_pColumnNames);  // creates browser controls
 
  setWindowTitle(windowCaption);  // sets window title
 
/*
  delete m_pModel;  // deletes pModel;
  delete m_pTableRecord;  // deletes m_pTableRecord
  // just to be sure
  m_pModel=0;
  m_pTableRecord=0;
*/
}

CBrowserWindow::CBrowserWindow(QWidget *parent, CDatabaseFoundation* pDatabase, QString sTableName, QString windowCaption)
 : QDialog(parent)
{
  m_pModel=new QSqlRelationalTableModel(parent);  // creates new model
  Q_CHECK_PTR(m_pModel);  // checks for succesful creation
  m_pModel->setTable(sTableName); // sets table name

  m_pColumnNames=new QStringList(); // creates new string list
  Q_CHECK_PTR(m_pColumnNames);  // checks for succesful creation

  // fetches record
  m_pTableRecord=new QSqlRecord(); // creates new record
  Q_CHECK_PTR(m_pTableRecord);  // checks for susccesful creation
  m_pTableRecord=&pDatabase->m_Database.record(sTableName); // fetches column names
  QSqlRecord tempRec=pDatabase->m_Database.record(sTableName); // fetches column names
  m_pTableRecord=new QSqlRecord(tempRec); // read column names
  Q_CHECK_PTR(m_pTableRecord);

  if (!m_pTableRecord->isEmpty()) {
    for (m_iIndex=0; m_iIndex<m_pTableRecord->count(); m_iIndex++) {
      m_pColumnNames->append(m_pTableRecord->fieldName(m_iIndex));
    }
  } // if

  createBrowserContens(this, pDatabase, m_pColumnNames);  // creates browser controls

  setWindowTitle(windowCaption);  // sets window title

/*
  delete m_pModel;  // deletes pModel;
  delete m_pTableRecord;  // deletes m_pTableRecord
  // just to be sure
  m_pModel=0;
  m_pTableRecord=0;
*/
}

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Here is also createBrowserContens(..):

void CBrowserWindow::createBrowserContens(QWidget* pParent, CDatabaseFoundation* pDatabase, QStringList* pColumnNames) {
  m_pHorizLayout=new QHBoxLayout();
  Q_CHECK_PTR(m_pHorizLayout);  // chechks creation of horiz layout
  m_pVertLayout=new QVBoxLayout();
  Q_CHECK_PTR(m_pVertLayout);  // checks creation of vertical layout
 
  m_pView=new QTableView(this);
  Q_CHECK_PTR(m_pView); // checks creation of view
 
  for(m_iIndex=0; m_iIndex<pColumnNames->count(); m_iIndex++) {
    pDatabase->m_pModel->setHeaderData(m_iIndex, Qt::Horizontal, m_pColumnNames->at(m_iIndex)); // sets column names
    qDebug() << m_iIndex << ": " << m_pColumnNames->at(m_iIndex);
    //pView->showColumn(m_iIndex);  // shows the selected column
  }
 
  m_pView->setModel(pDatabase->m_pModel); // sets model
  m_pView->setItemDelegate(new QSqlRelationalDelegate(m_pView));
 
  m_pButtonAdd=new QPushButton(QObject::trUtf8("Dodaj"));
  Q_CHECK_PTR(m_pButtonAdd);  // checks creation of pushbutton
 
  m_pButtonChange=new QPushButton(QObject::trUtf8("Spremeni"));
  Q_CHECK_PTR(m_pButtonChange);  // checks creation of pushbutton
 
  m_pButtonDelete=new QPushButton(QObject::trUtf8("Briši"));
  Q_CHECK_PTR(m_pButtonDelete);  // checks creation of pushbutton
 
  m_pButtonClose=new QPushButton(QObject::trUtf8("Zapri"));
  Q_CHECK_PTR(m_pButtonClose);
 
  // leyout setup
  m_pHorizLayout->addWidget(m_pButtonAdd);
  m_pHorizLayout->addWidget(m_pButtonChange);
  m_pHorizLayout->addWidget(m_pButtonDelete);
  m_pHorizLayout->addWidget(m_pButtonClose);
 
  m_pVertLayout->addWidget(m_pView);
 
  m_pVertLayout->addLayout(m_pHorizLayout);
 
  pParent->setLayout(m_pVertLayout);
 
  // button connectors
  connect(m_pButtonClose, SIGNAL(clicked()), this, SLOT(close()));
}

void CBrowserWindow::createBrowserContens(QWidget* pParent, CDatabaseFoundation* pDatabase, QStringList* pColumnNames) {
  m_pHorizLayout=new QHBoxLayout();
  Q_CHECK_PTR(m_pHorizLayout);  // chechks creation of horiz layout
  m_pVertLayout=new QVBoxLayout();
  Q_CHECK_PTR(m_pVertLayout);  // checks creation of vertical layout

  m_pView=new QTableView(this);
  Q_CHECK_PTR(m_pView); // checks creation of view

  for(m_iIndex=0; m_iIndex<pColumnNames->count(); m_iIndex++) {
    pDatabase->m_pModel->setHeaderData(m_iIndex, Qt::Horizontal, m_pColumnNames->at(m_iIndex)); // sets column names
    qDebug() << m_iIndex << ": " << m_pColumnNames->at(m_iIndex);
    //pView->showColumn(m_iIndex);  // shows the selected column
  }

  m_pView->setModel(pDatabase->m_pModel); // sets model
  m_pView->setItemDelegate(new QSqlRelationalDelegate(m_pView));

  m_pButtonAdd=new QPushButton(QObject::trUtf8("Dodaj"));
  Q_CHECK_PTR(m_pButtonAdd);  // checks creation of pushbutton

  m_pButtonChange=new QPushButton(QObject::trUtf8("Spremeni"));
  Q_CHECK_PTR(m_pButtonChange);  // checks creation of pushbutton

  m_pButtonDelete=new QPushButton(QObject::trUtf8("Briši"));
  Q_CHECK_PTR(m_pButtonDelete);  // checks creation of pushbutton

  m_pButtonClose=new QPushButton(QObject::trUtf8("Zapri"));
  Q_CHECK_PTR(m_pButtonClose);

  // leyout setup
  m_pHorizLayout->addWidget(m_pButtonAdd);
  m_pHorizLayout->addWidget(m_pButtonChange);
  m_pHorizLayout->addWidget(m_pButtonDelete);
  m_pHorizLayout->addWidget(m_pButtonClose);

  m_pVertLayout->addWidget(m_pView);

  m_pVertLayout->addLayout(m_pHorizLayout);

  pParent->setLayout(m_pVertLayout);

  // button connectors
  connect(m_pButtonClose, SIGNAL(clicked()), this, SLOT(close()));
}

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does NOT display data fields in window??

[harryf]

Are you calling select() on your model? setTableName() only populates the headers, but does not execute a query to fetch the data.

Also:

m_pTableRecord=&pDatabase->m_Database.record(sTableName); // fetches column names

this line is scary - you are taking the address of a temporary object. m_pTableRecord becomes a dangling pointer!

[MarkoSan]

Are you calling select() on your model? setTableName() only populates the headers, but does not execute a query to fetch the data.

Also:

m_pTableRecord=&pDatabase->m_Database.record(sTableName); // fetches column names

this line is scary - you are taking the address of a temporary object. m_pTableRecord becomes a dangling pointer!

I am dealing with this line right now, marcel helped me a lot with it. But for now, I've chcked, column names are fetched correctly. I will check now for select() method execution. Thanks a lot for now.

[MarkoSan]

I finally solved the problem, I had m_pModel on two different places (in CDatabaseFoundation and in CBrowserWindow). I've deleted the one in CBrowserWindow and works fine. For future references, what do you think, where should be m_pModel (QSqlRelationTableModel) declared in class that handles database connection or in class that handles record browsing?

[harryf]

A database model encapsulates a result set sent from the database. I would always keep it as local as possible (in your case, in the record browsing class) to prevent concurrency errors (e.g. when refactoring, two views might end up accessing the same model leading to strange race conditions).