QSqlDatabase as protected member results in "Driver not loaded"

Hi.

I'm trying to implement a generic connection class using Qt for my projects.

The code looks like this:

connection.h

Code:

---

#ifndef CONNECTION_H
#define CONNECTION_H
 
#include <QtSql/QSqlDatabase>
 
class Connection
{
    public:
        bool open();
        void close();
        bool isOpen() const;
 
        QString databaseName() const;
        QString hostName() const;
        QString userName() const;
        QString password() const;
        int port() const;
 
        QString lastError() const;
 
        operator QSqlDatabase();
        operator QSqlDatabase*();
 
    protected:
        void setDatabaseName(const QString &databaseName);
        void setHostName(const QString &hostName);
        void setUserName(const QString &userName);
        void setPassword(const QString &password);
        void setPort(int port);
 
    protected:
        QSqlDatabase m_db;
};
 
#endif // CONNECTION_H

---

connection.cpp

Code:

---

#include <QtSql/QSqlError>
 
#include "connection.h"
 
bool Connection::open()
{
    return m_db.open();
}
 
void Connection::close()
{
    if (isOpen())
        m_db.close();
}
 
bool Connection::isOpen() const
{
    return m_db.isOpen();
}
 
QString Connection::databaseName() const
{
    return m_db.databaseName();
}
 
QString Connection::hostName() const
{
    return m_db.hostName();
}
 
QString Connection::userName() const
{
    return m_db.userName();
}
 
QString Connection::password() const
{
    return m_db.password();
}
 
int Connection::port() const
{
    return m_db.port();
}
 
QString Connection::lastError() const
{
    return m_db.lastError().databaseText();
}
 
Connection::operator QSqlDatabase()
{
    return m_db;
}
 
Connection::operator QSqlDatabase *()
{
    return &m_db;
}
 
void Connection::setDatabaseName(const QString &databaseName)
{
    if (isOpen())
        close();
 
    if (m_db.databaseName() != databaseName)
        m_db.setDatabaseName(databaseName);
}
 
void Connection::setHostName(const QString &hostName)
{
    if (isOpen())
        close();
 
    m_db.setHostName(hostName);
}
 
void Connection::setUserName(const QString &userName)
{
    if (isOpen())
        close();
 
    m_db.setUserName(userName);
}
 
void Connection::setPassword(const QString &password)
{
    if (isOpen())
        close();
 
    m_db.setPassword(password);
}
 
void Connection::setPort(int port)
{
    if (isOpen())
        close();
 
    m_db.setPort(port);
}

---

sqliteconnection.h

Code:

---

#ifndef SQLITECONNECTION_H
#define SQLITECONNECTION_H
 
class Connection;
 
class SQLiteConnection : public Connection
{
    public:
        SQLiteConnection();
        SQLiteConnection(const QString &databaseName);
 
        bool open(const QString &databaseName);
};
 
#endif // SQLITECONNECTION_H

---

sqliteconnection.cpp

Code:

---

#include <QtCore/QUuid>
 
#include "connection.h"
#include "sqliteconnection.h"
 
SQLiteConnection::SQLiteConnection()
{
    m_db = QSqlDatabase::addDatabase("QSQLITE", QUuid::createUuid().toString());
}
 
SQLiteConnection::SQLiteConnection(const QString &databaseName)
{
    SQLiteConnection();
 
    Connection::setDatabaseName(databaseName);
}
 
bool SQLiteConnection::open(const QString &databaseName)
{
    Connection::setDatabaseName(databaseName);
 
    return Connection::open();
}

---

main.cpp

Code:

---

#include <QtWidgets/QApplication>
 
#include "monetae.h"
 
#include "db/connection.h"
#include "db/sqliteconnection.h"
#include "db/mysqlconnection.h"
 
#include <QtSql/QSqlQuery>
#include <QtCore/QDebug>
 
int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
 
    Connection con = SQLiteConnection("~/test.sq3");
 
    if (con.open() == false) {
        qDebug() << con.lastError();
 
        return -1;
    }
 
    QSqlQuery qry(con);
 
    qry.exec("CREATE TABLE TEST (ID INTEGER, NAME VARCHAR(10))");
 
    return 0;

---

The problem is that con.open() fails and con.lastError() returns "Driver not loaded". But if m_db is a private member in SqliteConnection and not a protected member in Connection everything works fine.

My guess is that you are not initializing m_db in the constructor you are using, only in the SQLiteConnection's default constructor.

I would recommend something like this so that this won't happen

Code:

---

class Connection
{
protected:
    Connection(const QString &driver, const QString &dbName)
        m_db(QSqlDatabase::addDatabase(driver, dbName))
    {
    }
};

---

Code:

---

SQLiteConnection::SQLiteConnection()
    : Connection("QSQLITE", QUuid::createUuid().toString())
{
}
 
SQLiteConnection::SQLiteConnection(const QString &databaseName)
    : Connection("QSQLITE", databaseName)
{
}

---

Cheers,
_

Many thanks anda_skoa!

You sugestion work like a charm.