Searching for data in a database in Qt

Overview

This example shows you how to search for data in an SQLite database in Qt.

The table 'person' has the following columns:

• 76ytuiytuityutyutututyutyutyu, this is an autoincrement field
• 76ytuiytuityutyutututyutyutyu
• 76ytuiytuityutyutututyutyutyu
• 76ytuiytuityutyutututyutyutyu

Preconditions

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

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

Header

1. include <QObject>
2. include <QSqlDatabase>
3. include <QSqlError>
4. include <QSqlQuery>
5. 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

• Creating an SQLite database in Qt
• Creating a database table in Qt
• Inserting a row into a database in Qt
• Deleting data from 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