Deleting data from a database in Qt

Article Metadata

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Tested with

Devices(s): Nokia 5800 XpressMusic, Nokia N900

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Compatibility

Platform(s): Qt

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Article

Keywords: QSqlDatabase, QSQlite, QSqlError, QSqlQuery

Created: tepaa (09 Sep 2009)

Last edited: hamishwillee (11 Oct 2012)

Overview

This example shows you how to delete data from an SQLite database in Qt.

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

• Qt is installed on your platform.
  • S60:
    • Download Qt release from here: Qt pre-release
    • Install Qt: How to Install Qt
    • Check this link for installation guide: How to install the package
    • Qt Tower release has SQLite support. The required libraries are built into the Qt release.
  • Maemo:
    • More information about Qt on Maemo can be found here: Qt4 Maemo port

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

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

Header

#include <QObject>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
#include <QString>
 
class DatabaseManager : public QObject
    {
    public:
        DatabaseManager(QObject *parent = 0);
        ~DatabaseManager();
 
    public:
        bool openDB();
        bool deletePerson(int id);
 
    private:
        QSqlDatabase db;
    };

Source

Delete a person from the database:

bool DatabaseManager::deletePerson(int id)
    {
    bool ret = false;
    if (db.isOpen())
        {
        QSqlQuery query;
        ret = query.exec(QString("delete from person where id=%1").arg(id));
        }
    return ret;
    }

The rest of the code:

bool DatabaseManager::openDB()
    {
    // Find QSLite driver
    db = QSqlDatabase::addDatabase("QSQLITE");
 
    #ifdef Q_OS_LINUX
    // NOTE: We have to store database file into user home folder in Linux
    QString path(QDir::home().path());
    path.append(QDir::separator()).append("my.db.sqlite");
    path = QDir::toNativeSeparators(path);
    db.setDatabaseName(path);
    #else
    // NOTE: File exists in the application private folder, in Symbian Qt implementation
    db.setDatabaseName("my.db.sqlite");
    #endif
 
    // Open databasee
    return db.open();
    }

Postconditions

A person's data is deleted from the database.

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
• Selecting data from a database without using SQL statements in Qt
• Using QDataWidgetMapper to show data from a database in Qt

• QtSql module