How to map a combobox with static items to database field?

Question

I've spent whole day looking for the answer (which I know exists, because I used it in the past but was lost).

I have this ordinary SQL table mapped to widgets on edit form. While I don't have problems with mapping to related SQL models, how can I create a mapping between DB field and a combobox with static, pre-set items?

I.e. 'gender' field holds 'M' or 'F', but the combobox shows either "Male" or "Female".

Answer 1

You can use QDataWidgetMapper::setItemDelegate and write QItemDelegate derived class that would handle the gender model column:

void ItemDelegate::setEditorData ( QWidget * editor, const QModelIndex & index ) const {
    if(index.column() == GenderColumnIndex) {
        QComboBox *combobox = qobject_cast<QComboBox*>(editor);
        Q_ASSERT(combobox);
        if(index.data().toString() == "M") {
           combobox->setCurrentIndex(0);
        } else {
           combobox->setCurrentIndex(1);
        }
    } else {
        QItemDelegate::setEditorData(editor, index);
    }
}
void ItemDelegate::setModelData ( QWidget * editor, QAbstractItemModel * model, const QModelIndex & index ) const {
    if(index.column() == GenderColumnIndex) {
        QComboBox *combobox = qobject_cast<QComboBox*>(editor);
        Q_ASSERT(combobox);
        if(combobox->currentIndex() == 0) {
           model->setData(index, "M");
        } else {
           model->setData(index, "F");
        }
    } else {
        QItemDelegate::setModelData(editor, model, index);
    }       
}    

OR

You can write a QComboBox derived class and define a custom property that QDataWidgetMapper can use to read/write the gender letter:

class QGenderComboBox : public QComboBox
{
    Q_OBJECT
    // If you set USER to true, you can omit the propertyName parameter
    // when you call QDataWidgetMapper::addMapping
    Q_PROPERTY(QString value READ value WRITE setValue USER true)

public:
    QGenderComboBox(QWidget *parent);

    // Sets the currentIndex from the gender letter
    void setValue(const QString);

    // Returns the letter from the currentIndex
    QString value() const;
};