Subclassing QSqlTableModel insert new value

Question

I want to show SQL data from a local db-File in a QML-Tableview and than would like to do some edits to the sql-database. What I managed to do after about three weeks: Showing my data in a QML-Tableview. I am not sure if I really need to subclass QSqlTableModel and I definitly would be glad if subclassing would not be neccessary at all.

In my main.cpp following should create my model and directly add a record.

    // Create an instance of the SqlModel for accessing the data
    SqlDataModel *sqlModel;
    sqlModel = new SqlDataModel(0,base.database());
    sqlModel->setTable("diaBaneDatabase");
    sqlModel->setSort(0, Qt::AscendingOrder);
    sqlModel->setEditStrategy(QSqlTableModel::OnFieldChange);

    sqlModel->select();


    QSqlRecord record(sqlModel->record());
    record.setValue(0,50);
    record.setValue(3,222);
    sqlModel->insertRecord(-1, record);
    sqlModel->submitAll();

This should add 222 to the 4th column. But nothing will be stored in my sqlDatabase

My SqlDataModel::setData loolks like this:

    bool SqlDataModel::setData(const QModelIndex &index, const QVariant &value, int role)
    {
        qDebug() << index.column() << "   " << index.row() << "   " << value << "   ----  " << role;


        qDebug() << roles[Qt::UserRole + 1];

        //qDebug() << QSqlTableModel::setData(modelIndex, value);

       qDebug() << QSqlQueryModel::setData(index, value);
        return false;

    }

The output will be:

    0     39     QVariant(int, 50)    ----   2
    "id"
    false
    1     39     QVariant(QString, "")    ----   2
    "id"
    false
    2     39     QVariant(QString, "")    ----   2
    "id"
    false
    3     39     QVariant(int, 222)    ----   2
    "id"
    false
    4     39     QVariant(double, 0)    ----   2
    "id"
    false
    5     39     QVariant(int, 0)    ----   2
    "id"
    false
    6     39     QVariant(double, 0)    ----   2
    "id"
    false
    7     39     QVariant(double, 0)    ----   2
    "id"
    false

For sure my setData method is wrong but I don't understand what should happen there and I didn't find any example for this.

Am I wrong with my assumption that I need to subclass QSqlTableModel to be able to put the model through QQmlContext to QML and than show the columns with roles named like my column-namings? If not how could I put the content of column 1 to QMLTableview:

        TableViewColumn {
            role: "id" // what should be the role if I don't subclass???
            title: "ID"
            width: 80
        }

I'm happy for any help, comment, example, other posts or whatever brings me further forward ... thanks

Answer 1

I've been working on an example.

Some notes:

• QML items such as TableView require a model so I think a QSqlTableModel is a very good option. Of course, you have other models that could be used to handle items of data.
• In the class MySqlTableModel you will see the required role names. MySqlTableModel reimplements roleNames() to expose the role names, so that they can be accessed via QML.
• You could reimplement the setData method in MySqlTableModel, but I think it is better to use the method insertRecord provided by QSqlTableModel.

I hope this example will help you to fix your errors.

main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "mysqltablemodel.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("mydb");

    if(!db.open()) {
        qDebug() << db.lastError().text();
        return 0;
    }

    QSqlQuery query(db);

    if(!query.exec("DROP TABLE IF EXISTS mytable")) {
        qDebug() << "create table error: " << query.lastError().text();
        return 0;
    }

    if(!query.exec("CREATE TABLE IF NOT EXISTS mytable \
                   (id integer primary key autoincrement, name varchar(15), salary integer)")) {
        qDebug() << "create table error: " << query.lastError().text();
        return 0;
    }

    MySqlTableModel *model = new MySqlTableModel(0, db);
    model->setTable("mytable");
    model->setEditStrategy(QSqlTableModel::OnManualSubmit);
    model->select();

    QSqlRecord rec = model->record();
    rec.setValue(1, "peter");
    rec.setValue(2, 100);
    model->insertRecord(-1, rec);
    rec.setValue(1, "luke");
    rec.setValue(2, 200);
    model->insertRecord(-1, rec);

    if(model->submitAll()) {
        model->database().commit();
    } else {
        model->database().rollback();
        qDebug() << "database error: " << model->lastError().text();
    }

    QQmlApplicationEngine engine;

    QQmlContext *ctxt = engine.rootContext();
    ctxt->setContextProperty("myModel", model);

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

mysqltablemodel.h

#ifndef MYSQLTABLEMODEL_H
#define MYSQLTABLEMODEL_H

#include <QSqlTableModel>
#include <QSqlRecord>
#include <QSqlError>
#include <QSqlQuery>
#include <QDebug>

class MySqlTableModel : public QSqlTableModel
{
    Q_OBJECT

public:
    MySqlTableModel(QObject *parent = 0, QSqlDatabase db = QSqlDatabase());
    Q_INVOKABLE QVariant data(const QModelIndex &index, int role=Qt::DisplayRole ) const;
    Q_INVOKABLE void addItem(const QString &name, const QString &salary);

protected:
    QHash<int, QByteArray> roleNames() const;

private:
    QHash<int, QByteArray> roles;
};

#endif // MYSQLTABLEMODEL_H

mysqltablemodel.cpp

#include "mysqltablemodel.h"

MySqlTableModel::MySqlTableModel(QObject *parent, QSqlDatabase db): QSqlTableModel(parent, db) {}

QVariant MySqlTableModel::data ( const QModelIndex & index, int role ) const
{
    if(index.row() >= rowCount()) {
        return QString("");
    }
    if(role < Qt::UserRole) {
        return QSqlQueryModel::data(index, role);
    }
    else {
        return QSqlQueryModel::data(this->index(index.row(), role - Qt::UserRole), Qt::DisplayRole);
    }
}

QHash<int, QByteArray> MySqlTableModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[Qt::UserRole + 1] = "name";
    roles[Qt::UserRole + 2] = "salary";
    return roles;
}

void MySqlTableModel::addItem(const QString &name, const QString &salary)
{
    QSqlRecord rec = this->record();
    rec.setValue(1, name);
    rec.setValue(2, salary.toInt());
    this->insertRecord(-1, rec);

    if(this->submitAll()) {
        this->database().commit();
    } else {
        this->database().rollback();
        qDebug() << "database error: " << this->lastError().text();
    }
}

main.qml

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Window 2.2
import QtQuick.Dialogs 1.2

ApplicationWindow {
    title: qsTr("Hello World")
    width: 640
    height: 480
    visible: true

    TableView {
        id: tableView

        anchors.fill: parent

        TableViewColumn {
            role: "name"
            title: "Name"
            width: 200
        }

        TableViewColumn {
            role: "salary"
            title: "Salary"
            width: 200
        }

        model: myModel
    }

    Button {
        id: addButton

        anchors.verticalCenter: parent.verticalCenter

        text: "Add item"

        onClicked: {
            if (nameBox.text || salaryBox.text) {
                myModel.addItem(nameBox.text, salaryBox.text)
            }
        }
    }
    TextField {
        id: nameBox
        placeholderText: "name"

        anchors.verticalCenter: parent.verticalCenter
        anchors.left: addButton.right
        anchors.leftMargin: 5
    }

    TextField {
        id: salaryBox
        placeholderText: "salary"

        anchors.verticalCenter: parent.verticalCenter
        anchors.left: nameBox.right
        anchors.leftMargin: 5
    }
}