Errors in subclass of QSqlRelationalDelegate

[Christian Ehrlicher]

@Panoss said in Errors in subclass of QSqlRelationalDelegate:

isinstance

What does this function do / where is it defined? You for sure want to use qobject_cast<>() instead.

[Panoss]

@Christian-Ehrlicher said in Errors in subclass of QSqlRelationalDelegate:

use qobject_cast<>() instead.

I did it this way:

qobject_cast <QComboBox*>(editor )){
editor->model().select();

The error from the first line is gone.
On the second I get:
'bookdelegate.cpp:133:21: error: no member named 'model' in 'QWidget''

[Christian Ehrlicher]

@Panoss said in Errors in subclass of QSqlRelationalDelegate:

qobject_cast <QComboBox*>(editor )){

And what should this help? You should assign the return value to a variable. c basics.

[Panoss]

@Christian-Ehrlicher
What I 'm actually trying to do is convert this python code to Qt c++:

    def createEditor(self, parent, option, index):
        # column of combo box 'position'
        positionColumn = 2
        print("myDelegate.createEditor index.column()=" + str(index.column()) + " option=" + str(option) )
        if index.column() == positionColumn:
            editor = QSqlRelationalDelegate.createEditor(self, parent, option, index)
            if isinstance(editor, QComboBox):
                editor.model().select()
            return editor
        else:
            return super(myDelegate, self).createEditor(parent, option, index)

[Christian Ehrlicher]

Learning the very basics of c++ is not part of this forum. Doing a simple assignment of a function call to a variable is really not that hard.

[Panoss]

You mean this?

QComboBox* mycombo = qobject_cast <QComboBox*>(editor );

[Panoss]

This is the code I ended up with (from the QSqlRelationalDelegate 's code), and works!
Any comments are welcome.

    int positionColumn = 2;
    qDebug()<< "BookDelegate.createEditor index.column()=" << (index.column()) << " option=" << option ;
    if (index.column() == positionColumn){
        const QSqlRelationalTableModel *sqlModel = qobject_cast<const QSqlRelationalTableModel *>(index.model());
        QSqlTableModel *childModel = sqlModel ? sqlModel->relationModel(index.column()) : nullptr;
        if (!childModel)
            return QStyledItemDelegate::createEditor(parent, option, index);

        QComboBox *combo = new QComboBox(parent);
        combo->setModel(childModel);
        combo->setModelColumn(1);
        combo->installEventFilter(const_cast<BookDelegate *>(this));
        childModel->select();
        return combo;
    }

[JonB]

@Panoss said in Errors in subclass of QSqlRelationalDelegate:

        editor = QSqlRelationalDelegate.createEditor(self, parent, option, index)
        if isinstance(editor, QComboBox):
            editor.model().select()
        return editor

QWidget *editor = QSqlRelationalDelegate::createEditor(parent, option, index);
QComboBox *combo = qobject_cast<QComboBox *>(editor);
if (combo)
     combo->model()->select();
return editor;

[Panoss]

@JonB said in Errors in subclass of QSqlRelationalDelegate:

return editor;

Should I return the editor or the combo?

[JonB]

@Panoss
Since I wrote return editor; and not return combo; you have the answer :)

But you should understand why this is. No matter what editor = QSqlRelationalDelegate::createEditor(), which is what you want to return under all circumstances. combo only has a != nullptr value if editor is a QComboBox * --- i.e. the createEditor() returned a QWidget which is a QComboBox --- and of course in that case editor == combo anyway. But if, for whatever reason, editor is not combobox/QComboBox * --- presumably for a column which is not the foreign key column but some other column --- you still want to return whatever that editor is.

My C++ is a direct translation of the original Python, which I presume to be correct/desired, unless you want to change that behaviour for some reason.

[Panoss]

@JonB (and to all of course) thank you for your time and effort!
In python it works fine, I will try your code but I am sure it's fine!