Handling QSqlDatabase connections - c++

Question

What is the correct way to handle connections for QSqlDatabase?
In my program I am doing it this way:
DatabaseConnector *databaseConnector = 0;
try
{
databaseConnector = new DatabaseConnector();
//Do stuff...
delete databaseConnector;
}
catch(QString e)
{
delete databaseConnector;
QMessageBox::information(this,"Error",e);
}
databaseConnector.h
#ifndef DATABASECONNECTOR_H
#define DATABASECONNECTOR_H
#include <QtSql>
class DatabaseConnector
{
public:
DatabaseConnector();
DatabaseConnector(QString hostname, QString database, QString user, QString password);
~DatabaseConnector();
private:
QSqlDatabase db;
};
#endif // DATABASECONNECTOR_H
databaseconnector.cpp
#include "databaseconnector.h"
#include <QString>
DatabaseConnector::DatabaseConnector()
{
QSettings settings;
db = QSqlDatabase::addDatabase("QIBASE");
db.setHostName(settings.value("db/host").toString());
db.setDatabaseName(settings.value("db/name").toString());
db.setUserName(settings.value("db/user").toString());
db.setPassword(settings.value("db/pass").toString());
if(!db.open())
{
QString databaseConnectionError = db.lastError().text();
throw databaseConnectionError;
}
}
DatabaseConnector::DatabaseConnector(QString hostname, QString database, QString user, QString password)
{
db = QSqlDatabase::addDatabase("QIBASE");
db.setHostName(hostname);
db.setDatabaseName(database);
db.setUserName(user);
db.setPassword(password);
if(!db.open())
{
QString databaseConnectionError = db.lastError().text();
throw databaseConnectionError;
}
}
DatabaseConnector::~DatabaseConnector()
{
db.close();
}
I'm getting error even if I use QSqlDatabase::removeDatabase(db.connectionName());
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

Answer 1

Normally you don’t need to open the database connection more than once within your application.
When adding a database, you can name the connection :
QSqlDatabase::addDatabase( "QIBASE", "MyDBConnectionName" );
You can use the name to query for the connection :
if( QSqlDatabase::contains( "MyDBConnectionName" ) )
{
QSqlDatabase db = QSqlDatabase::database( "MyDBConnectionName" );
//Do stuff...
}
else
{
// connection not found, do something
}
Also notice that before calling QSqlDatabase::removeDatabase you should disconnect your database :
db.close();
QSqlDatabase::removeDatabase("MyDBConnectionName");

Answer 2

In order to add a new database, you need to give it a name. If you do not give a unique name, the default database is re-used. This is documented in the class reference.
Try:
db = QSqlDatabase::addDatabase("QIBASE", databaseName);

Answer 3

In main app:
QSqlDatabase db =QSqlDatabase::addDatabase( "QSQLITE");
in second app:
QSqlDatabase db2 =QSqlDatabase::database();