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Searching for data in a database in Qt

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Article Metadata
Tested with
SDK: Qt "Tower" pre-release
Devices(s): Nokia 5800 XpressMusic, Nokia N900
Compatibility
Platform(s): Qt
Symbian
Article
Keywords: QSqlDatabase, QSQlite, QSqlError, QSqlQuery
Created: tepaa (25 Nov 2009)
Last edited: hamishwillee (11 Oct 2012)

Contents

Overview

This example shows you how to search for data in 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

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 PersonData
{
public:
int id;
QString firstname;
QString lastname;
int age;
};
 
 
class DatabaseManager : public QObject
{
public:
DatabaseManager(QObject *parent = 0);
~DatabaseManager();
 
public:
bool openDB();
bool getPerson(int id, PersonData*& person);
 
private:
QSqlDatabase db;
};


Source

Search for person data from the database:

bool DatabaseManager::getPerson(int id, PersonData*& person)
{
bool ret = false;
 
QSqlQuery query(QString("select * from person where id = %1").arg(id));
if (query.next())
{
person->id = query.value(0).toInt();
person->firstname = query.value(1).toString();
person->lastname = query.value(2).toString();
person->age = query.value(3).toInt();
ret = true;
}
 
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

Person data is searched from the database.


See also

This page was last modified on 11 October 2012, at 04:18.
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