void MainWindow::updateListAuto()
{
    modelListAuto = new QSqlRelationalTableModel(viewListAuto);
    modelListAuto->setTable("list_cars");
    modelListAuto->setEditStrategy(QSqlTableModel::OnFieldChange);
    modelListAuto->setJoinMode(QSqlRelationalTableModel::LeftJoin);
    modelListAuto->setRelation(modelListAuto->fieldIndex("car_id"), QSqlRelation("cars", "id", "name AS car_name"));
    modelListAuto->setRelation(modelListAuto->fieldIndex("task_id"), QSqlRelation("tasks", "id", "name AS task_name"));
    modelListAuto->select();
    viewListAuto->setModel(modelListAuto);
    viewListAuto->show();
}

..
{
    QModelIndex index = viewListAuto->selectionModel()->currentIndex();
    ListAuto * dlg = new ListAuto(this,"edit"); // диалоговое окно с редактированием
    dlg->setAttribute(Qt::WA_DeleteOnClose);
    dlg->setModel(modelListAuto);//отправляем модель
    dlg->mapper->setCurrentModelIndex(index);//текущий индекс 
    dlg->exec();
}
..

void ListAuto::setModel(QSqlRelationalTableModel *model)
{


    QSqlTableModel *modelTask = model->relationModel(model->fieldIndex("task_name"));
    ui->task->setModel(modelTask);
    ui->task->setModelColumn(modelTask->fieldIndex("name"));

    QSqlTableModel *modelCar = model->relationModel(model->fieldIndex("car_name"));
    ui->car->setModel(modelCar);
    ui->car->setModelColumn(modelCar->fieldIndex("name"));

    mapper->setModel(model);
    mapper->setItemDelegate(new QSqlRelationalDelegate(this));
    mapper->addMapping(ui->dateEdit,model->fieldIndex("date"));
    mapper->addMapping(ui->task,model->fieldIndex("task_name"));
    mapper->addMapping(ui->car,model->fieldIndex("car_name"));
}
void ListAuto::done(int r)
{
    if(QDialog::Accepted == r) {
        if(_mode == "add" and mapper->submit()) {
            QDialog::done(r);
            return;
        }
        else if(_mode == "edit" and mapper->submit() ){
            QDialog::done(r);
            return;
        }
        else {
            QMessageBox::critical(this,tr("Error"),tr("Error %1 list").arg(_mode == "add" ? "adding" : "editing"));
            return;
        }
    }
    else {
        QDialog::done(r);
        return;
    }
}