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QSqlRelationalTableModel Dopdown List for Field

  • Hello,
    I want in a qtableview (DamTV) a Dropdown-Listbox for a special column.

    QSqlRelationalTableModel Dams;
    Dams.setRelation(4, QSqlRelation("qlkp_DamPart", "ID", "SCDesc"));
    ui->DamTV->setItemDelegateForColumn(4, new QSqlRelationalDelegate(this));;

    After select all is correct, I see instead of the primary key the lookup text in column 4.
    When I select a field and leave the field I see the primary key (ID).

    Why is that ? Why changes the editor the view representation of the data ?
    This should be independent when I understand the concept correctly.

  • Lifetime Qt Champion


    Where are you using this code ?

  • @SGaist
    In the constructor of the dialog after ui->setupUi(this);
    QSqlRelationalTableModel Dams; is of course in the header of the dialog.

  • Lifetime Qt Champion

    Which OS and Qt version ?

  • Qt 5.6.0 32-bit, MSVC 2015, Windows 10 64-bit

    If found the code for the QSqlRelationalDelegate, have made a renamed copy of it for testing.

    class QSqlRelationalDelegate2: public QItemDelegate
        explicit QSqlRelationalDelegate2(QObject *aParent = 0)
            : QItemDelegate(aParent)  {}
        ~QSqlRelationalDelegate2()  {}
        QWidget *createEditor(QWidget *aParent,
                              const QStyleOptionViewItem &option,
                              const QModelIndex &index) const
            const QSqlRelationalTableModel *sqlModel
                    = qobject_cast<const QSqlRelationalTableModel *>(index.model());
            QSqlTableModel *childModel = sqlModel ? sqlModel->relationModel(index.column()) : 0;
            if (!childModel)
                return QItemDelegate::createEditor(aParent, option, index);
            QComboBox *combo = new QComboBox(aParent);
            combo->installEventFilter(const_cast<QSqlRelationalDelegate2 *>(this));
            return combo;
        void setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const
            if (!index.isValid())
            QSqlRelationalTableModel *sqlModel = qobject_cast<QSqlRelationalTableModel *>(model);
            QSqlTableModel *childModel = sqlModel ? sqlModel->relationModel(index.column()) : 0;
            QComboBox *combo = qobject_cast<QComboBox *>(editor);
            if (!sqlModel || !childModel || !combo) {
                QItemDelegate::setModelData(editor, model, index);
    //        QSqlRelation newrel(sqlModel->relation(index.column()));
            int currentItem = combo->currentIndex();
            int childColIndex = childModel->fieldIndex(sqlModel->relation(index.column()).displayColumn());
            int childEditIndex = childModel->fieldIndex(sqlModel->relation(index.column()).indexColumn());
            QString dd=childModel->data(childModel
                    ->index(currentItem, childColIndex), Qt::DisplayRole).toString();
                    childModel->data(childModel->index(currentItem, childColIndex),
                    Qt::DisplayRole), Qt::DisplayRole);
                    childModel->data(childModel->index(currentItem, childEditIndex),
                    Qt::EditRole), Qt::EditRole);
    //        sqlModel->setRelation(index.column(), newrel);
    //        sqlModel->dataChanged(index, index,
    //                QVector<int>()<<Qt::DisplayRole<<Qt::EditRole);
        void paint(QPainter* painter,   const QStyleOptionViewItem& opt,
                   const QModelIndex& index) const
            QStyleOptionViewItem so=opt;
            drawDisplay(painter, so, so.rect, s);

    Not even the overwriting of the paint function help. Should not have the delegate the control for the painting always ?

    In the setModelData function the last command

                    childModel->data(childModel->index(currentItem, childEditIndex),
                    Qt::EditRole), Qt::EditRole);

    makes the problem. After write back the data from the widget to the model I get the view shows the foreign key and not its lookup.

  • I found the delegate has indeed ever the control for the painting. Before editing all works.
    The problem is that after setModelData both the Display- and Editrole give always the foreign key for the changed cell.


  • Lifetime Qt Champion

    Can you provide a minimal compilable example that reproduce that behaviour ?

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