inherit from QSqlDatabase

[RogerWilco77]

Good afternoon,

I guess it is more a c++ beginner's question than actually Qt releated. So it probably fits best here:

I want to access a MySql database. Everything is working fine. To get a better structure I wanted to have my database interactions in one class:

MyDatabase

Ok, so why not inherit from QSqlDatabase and extend with the needed additional members:



#ifndef MYDATABASE_H
#define MYDATABASE_H

#include <QSqlDatabase>

class MyDatabase : public QSqlDatabase
{

public:
MyDatabase();
};

#endif // MYDATABASE_H


If I now want to create a connection with:


mydb = MyDatabase::addDatabase("QMYSQL")

I get the message:


./Stromverbrauch/mainwindow.cpp: In member function 'int MainWindow::connectDatabase()':
../Stromverbrauch/mainwindow.cpp:33:44: error: no match for 'operator=' in '((MainWindow*)this)->MainWindow::mydb = QSqlDatabase::addDatabase(const QString&, const QString&)((* & QString((*(const QLatin1String*)(& QLatin1String(QSqlDatabase::defaultConnection))))) )'
../Stromverbrauch/mainwindow.cpp:33:44: note: candidate is:
In file included from ../Stromverbrauch/mainwindow.h:25:0,
from ../Stromverbrauch/mainwindow.cpp:1:
../Stromverbrauch/mydatabase.h:6:7: note: MyDatabase& MyDatabase::operator=(const MyDatabase&)
../Stromverbrauch/mydatabase.h:6:7: note: no known conversion for argument 1 from 'QSqlDatabase' to 'const MyDatabase&'

Ok, I have read somewhere in a different forum the advice to reimplement the "addDatabase" function.
But why is this necessary? Shoud the child not inheric also static functions?
What am I missing to understand the issue?

I am looking forward for your advice.

RogerWilco77

[wysota]

It's probably a bad idea at all to try and subclass QSqlDatabase. It is much better and easier to create your own class that accepts QSqlDatabase as a parameter, stores it as a private member and uses it to operate on the database where required.

[RogerWilco77]

Thanks for the advice.
I will follow it. Still it seems like I have something not understood regarding static functions.
Have a nice weekend.