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QSqlRelationalTableModel doesn't give relation foreign key with Qt::EditRole



  • Consider the Qt's example "RelationalTableModel".

    #include <QtWidgets>
    #include <QtSql>
    
    #include "../connection.h"
    #include <QDebug>
    
    #include <memory>
    
    void initializeModel(QSqlRelationalTableModel *model)
    {
    //! [0]
        model->setTable("employee");
    //! [0]
    
        model->setEditStrategy(QSqlTableModel::OnManualSubmit);
    //! [1]
        model->setRelation(2, QSqlRelation("city", "id", "name"));
    //! [1] //! [2]
        model->setRelation(3, QSqlRelation("country", "id", "name"));
    //! [2]
    
    //! [3]
        model->setHeaderData(0, Qt::Horizontal, QObject::tr("ID"));
        model->setHeaderData(1, Qt::Horizontal, QObject::tr("Name"));
        model->setHeaderData(2, Qt::Horizontal, QObject::tr("City"));
        model->setHeaderData(3, Qt::Horizontal, QObject::tr("Country"));
    //! [3]
    
        model->select();
    }
    
    std::unique_ptr<QTableView> createView(const QString &title, QSqlTableModel *model)
    {
    //! [4]
        std::unique_ptr<QTableView> view{new QTableView};
        view->setModel(model);
        view->setItemDelegate(new QSqlRelationalDelegate(view.get()));
    //! [4]
        view->setWindowTitle(title);
    
        QObject::connect(view.get()->selectionModel(), &QItemSelectionModel::selectionChanged,
                         [=](const QItemSelection &selected, const QItemSelection &deselected){
            for (const QModelIndex &idx : selected.indexes()) {
                qDebug() << "DisplayRole:" << model->index(idx.row(), idx.column(), QModelIndex()).data(Qt::DisplayRole);
                qDebug() << "EditRole" << model->index(idx.row(), idx.column(), QModelIndex()).data(Qt::EditRole);
            }
            qDebug() << '\n';
        });
    
        return view;
    }
    
    void createRelationalTables()
    {
        QSqlQuery query;
        query.exec("create table employee(id int primary key, name varchar(20), city int, country int)");
        query.exec("insert into employee values(1, 'Espen', 5000, 47)");
        query.exec("insert into employee values(2, 'Harald', 80000, 49)");
        query.exec("insert into employee values(3, 'Sam', 100, 1)");
    
        query.exec("create table city(id int, name varchar(20))");
        query.exec("insert into city values(100, 'San Jose')");
        query.exec("insert into city values(5000, 'Oslo')");
        query.exec("insert into city values(80000, 'Munich')");
    
        query.exec("create table country(id int, name varchar(20))");
        query.exec("insert into country values(1, 'USA')");
        query.exec("insert into country values(47, 'Norway')");
        query.exec("insert into country values(49, 'Germany')");
    }
    
    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
        if (!createConnection())
            return EXIT_FAILURE;
    
        createRelationalTables();
    
        QSqlRelationalTableModel model;
    
        initializeModel(&model);
    
        std::unique_ptr<QTableView> view = createView(QObject::tr("Relational Table Model"), &model);
        view->show();
    
        return app.exec();
    }
    

    I've added some debug code into the "createView" function.
    When I run the application and select, for example, the cell on the first row and the "City" column in the table, I get the following message in the console:
    DisplayRole: QVariant(QString, "Oslo")
    EditRole QVariant(QString, "Oslo")

    Then I double-click that cell and in the combo-box, I change the city to "San Jose", for example, and again select this cell. Now I get another message in the console:
    DisplayRole: QVariant(QString, "San Jose")
    EditRole QVariant(qlonglong, 100)
    .
    As you can see, now the "EditRole" flag allows us to get the ID of a city in the relational table. But one cannot obtain that ID not changing the value in the cell.
    How can I get that ID at once, not changing manually values in such cells?


  • Lifetime Qt Champion

    Hi,

    You can use the model returned by QRelationalTableModel::relationModel to get the information you seek.


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