Using QDataWidgetMapper to show data from a database in Qt

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Article Metadata

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Tested with

SDK: Qt "tower" pre-release

Devices(s): Nokia 5800 XpressMusic, Nokia N900

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Compatibility

Platform(s): Qt

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Article

Keywords: QSqlDatabase, QSQlite, QSqlTableModel, QDataWidgetMapper

Created: tepaa (25 Nov 2009)

Last edited: hamishwillee (11 Oct 2012)

Overview

This example shows you how to map a UI component to a database table using QSqlTableModel and QDataWidgetMapper in Qt. Searching and updating data can be done without using any SQL statements.

The table 'person' has the following columns:

• id (integer primary key), this is an autoincrement field
• firstname (varchar(20))
• lastname (varchar(30))
• age (integer)

Preconditions

For Maemo SQLite development, the following packages must be installed:

• libqt4-sql
• libqt4-sql-sqlite
• libsqlite3-0
• libsqlite3-dev

Header

Dialog for showing and updating a person's last name:

#include <QtGui>
#include <QtSql>
 
class MyDialog : public QDialog
    {
    Q_OBJECT
 
    public:
        MyDialog(int id = 0, QWidget *parent = 0);
        ~MyDialog();
 
    public slots:
        void save();
 
    private:
        // "person" table mode class
        QSqlTableModel*             tableModel;
 
        // Maps QLineEdit ui control into "person"
        // table's lastname field
        QDataWidgetMapper*          dataMapper;
 
        QVBoxLayout*                vboxlayout;
        QLineEdit*                  nameLineEdit;
        QPushButton*                saveButton;
    };

Source

MyDialog::MyDialog(int id, QWidget *parent)
    : QDialog(parent)
    {
    vboxlayout = new QVBoxLayout(this);
 
    nameLineEdit = new QLineEdit(this);
    nameLineEdit->setContextMenuPolicy(Qt::NoContextMenu);
    nameLineEdit->setAlignment(Qt::AlignTop);
    vboxlayout->addWidget(nameLineEdit);
 
    saveButton = new QPushButton("Save",this);
    saveButton->setFixedHeight(60);
    QObject::connect(saveButton, SIGNAL(clicked()), this, SLOT(save()));
    vboxlayout->addWidget(saveButton);
 
    // 'person' table model
    tableModel = new QSqlTableModel(this);
    tableModel->setTable("person");
    // Set where clause
    // QLineEdit shows person lastname that id is given parameter
    tableModel->setFilter(QString("id=%1").arg(id));
    tableModel->select();
 
    // Maps QLineEdit ui control into "person" table's lastname field
    dataMapper = new QDataWidgetMapper(this);
    dataMapper->setModel(tableModel);
    // We want that data is stored only if we call QDataWidgetMapper::submit()
    dataMapper->setSubmitPolicy(QDataWidgetMapper::ManualSubmit);
    dataMapper->setItemDelegate(new QSqlRelationalDelegate(dataMapper));
    dataMapper->addMapping(nameLineEdit, tableModel->fieldIndex("lastname"));
    dataMapper->toFirst();
 
    setLayout(vboxlayout);
    }
 
MyDialog::~MyDialog()
    {
    }
 
 
void MyDialog::save()
    {
    // Stores data from QLineEdit to database using QDataWidgetMapper
    dataMapper->submit();
    }

Postconditions

The UI controls get data from the database and the data can be updated via controls without using any SQL statements.

See also

• Creating an SQLite database in Qt
• Creating a database table in Qt
• Inserting a row into a database in Qt
• Searching for data in a database in Qt
• Deleting data from a database in Qt
• Selecting data from a database without using SQL statements in Qt

• QDataWidgetMapper
• QtSql module