[Qt-interest] Custom SQLite Driver

[Neville Dastur]

Thanks for the suggestions. The invoke method thing works for the 
driver, but I also then needed to modify the QSQLiteResult class which 
is not a Q_OBJECT and so neither method works.

So the solution that seems to work so far is to set a flag using 
Q_PROPERTY in the driver, then in QSQLiteResult test for the flag and 
act accordingly.

class Q_EXPORT_SQLDRIVER_SQLITE QSQLiteDriver : public QSqlDriver

{

    Q_OBJECT

    Q_PROPERTY(bool ExecNoReturn READ getExecNoReturn WRITE setExecNoReturn)

....

private:

    // Property Functions

    bool ExecNoReturn;

    bool getExecNoReturn() { return ExecNoReturn; };

    void setExecNoReturn(bool flag) {ExecNoReturn=flag;};

private:

    QSQLiteDriverPrivate* d;

};

bool QSQLiteResult::reset(const QString &query)

{

    // Perform as a sqlite3_exec() instead if property flag set, but reset on each use

    QVariant ret = this->driver()->property("ExecNoReturn");

    if (ret.isValid() & ret.toBool()) {

        QSqlDriver *d = const_cast<QSqlDriver *>(driver());

        d->setProperty("ExecNoReturn", QVariant::fromValue(false));

        return this->_execNoReturnSet(query);

    }

    else {

        if (!prepare(query))

            return false;

        return exec();

    }

}

then in the QSQLiteResult class we have:

bool QSQLiteResult::_execNoReturnSet(const QString &query) {

    if (!driver() || !driver()->isOpen() || driver()->isOpenError())

        return false;

    char* localError=0;

    int res = sqlite3_exec((sqlite3*) d->access, query.toLocal8Bit().constData(), 0, 0, &localError);

    if (res != SQLITE_OK) {

        setLastError(qMakeError(d->access, QCoreApplication::translate("QSQLiteResult",

                     "Unable to execute statement using sqlite3_exec"), QSqlError::StatementError, res));

        return false;

    }

    return true;

}

In the calling source we do:
QSqlQuery q;
QSqlDriver *d = const_cast<QSqlDriver *>(q.driver());
d->setProperty("ExecNoReturn", QVariant::fromValue(true));
q.exec(SQL_CREATE_DB);


Again, just posting this to find out if there is a better solution. Also 
might help someone else.

The underlying problem here is that the current SQLite driver won't 
handle SQL with multiple statements i.e. separated by ; so wanted a way 
to use the sqlite3_exec function.



André Somers wrote:
> Would it be sensible to express the key as a property? In that case, you
> could use setProperty("key") on your driver, and loose the conversion. Check
> out Q_PROPERTY to see how. Perhaps slightly less hackish than using
> invokeMethod(), though I use that approach myself quite frequently.
>
> André
>
>
> -----Oorspronkelijk bericht-----
> Van: qt-interest-bounces at trolltech.com
> [mailto:qt-interest-bounces at trolltech.com] Namens Mohammed Sameer
> Verzonden: zondag 29 november 2009 14:25
> Aan: qt-interest at trolltech.com
> Onderwerp: Re: [Qt-interest] Custom SQLite Driver
>
> I'm not an expert here but...
>
> On Sun, Nov 29, 2009 at 12:03:16PM +0000, Neville Dastur wrote:
>   
>> I am writing a custom SQLite driver to use the encryption routines from 
>> wxSqlite. I have got the whole thing compiling and working by following 
>> the docs on writing your own driver 
>> (http://qt.nokia.com/doc/4.5/qsqldatabase.html#addDatabase-2) , but I am 
>> having a problem including a new method.
>>
>> To set a password on the database the ReKey function needs to be called. 
>> I created a public method:
>>  void QSQLiteDriver::ReKey(const QString & key)
>>
>> When calling QSQLDatabase m_db->driver()->ReKey("test"); the function 
>> ReKey can't be found.
>>  and
>>
>> QSQLiteDriver *driver = m_db->driver();
>> driver->ReKey("test");
>>     
>
> QSQLiteDriver *driver = dynamic_cast<QSQLiteDriver *>(m_db->driver()); //
> Some might prefer qobject_cast
>
>   
>> What is this the best way of adding new functionality to a QSQLDriver.
>>     
>
> Maybe a public slot and then use QMetaObject::invokeMethod() ?
>
> Sounds ugly but I can't find something else ;-)
>
> Cheers,
>
>   
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