Handling QSqlDatabase connections

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.

Nejat · Accepted Answer · 2014-08-25 10:06:51Z

6

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");

answered Aug 25, 2014 at 10:06

Nejat

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1 Comment

Sajmplus Over a year ago

I have problem with that, when i add DatabaseConnectionName and remove it in destructor after db.close() i'm getting two errors: QSqlDatabasePrivate::removeDatabase: connection 'fbc' is still in use, all queries will cease to work. and QSqlQuery::prepare: database not open

RobbieE · Accepted Answer · 2014-08-25 10:07:49Z

0

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);

answered Aug 25, 2014 at 10:07

RobbieE

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Comments

Ajean · Accepted Answer · 2016-08-10 16:08:19Z

-2

In main app:

QSqlDatabase db =QSqlDatabase::addDatabase( "QSQLITE");

in second app:

QSqlDatabase db2 =QSqlDatabase::database();

edited Aug 10, 2016 at 16:08

Ajean

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answered Aug 10, 2016 at 7:20

Adrian

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