Extending a plugin in a static library

[ultim8]

Hello ultim8,

I am haven a similar issue, and I found your post. So I wanted to ask you how you eventually solved it?

Regards,
Davor

Davor,

I decided to go with my original method of compiling the QPSQL Driver as a library. I can't remember the road blocks that got in my way, but I could not find a suitable way of transparently making it "just work" no matter if the Driver was a plugin or a library.

Really though, it has not been an issue to compile the QPSQL Driver as a library... the only downside is I have not been able to use the pre-built SDK's... but have had to compile Qt myself.

If you end up coming up with a method that works for you, I would love to hear about it.

[Davor]

Ultim8,

Good to know that at least the library version works!

I gave up and worked around it: QSqlDatabase::driver() will give you QPSQLDriver. With the handle you can extract PGconn, and PGconn you can use with functions from pglib.dll. This way you can implement extra functionality.


Here some brainstorming to make subclassing work with QPSQLDriver as plugin for those interested:

If you compiled the driver as a plugin, then QPSQLDriver* drv = new QPSQLDriver(); or any subclass of QPSQLDriver will give you “undefined reference” errors. But you can initialize one with the following code:

QPluginLoader l("W:/dev/Qt/4.6.0/plugins/sqldrivers/qsqlpsqld4.dll");
    QSqlDriverPlugin *o = qobject_cast<QSqlDriverPlugin*>(l.instance());
    QPSQLDriver *d = dynamic_cast<QPSQLDriver*>(o->create("QPSQL"));

QPluginLoader l("W:/dev/Qt/4.6.0/plugins/sqldrivers/qsqlpsqld4.dll");
    QSqlDriverPlugin *o = qobject_cast<QSqlDriverPlugin*>(l.instance());
    QPSQLDriver *d = dynamic_cast<QPSQLDriver*>(o->create("QPSQL"));

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Trolls use a factory pattern throughout the driver creation code as far as I see. So QPSQLDriverPlugin::create() is called to produce an instance of QPSQLDriver. Now if one could use the output of QPSQLDriverPlugin::create() as a base class, then one could extend QPSQLDriver, no?

Currently, I don't see a way to do it. But then again, wouldn't something like this be farfetched? Creating a custom plugin, based on QPSQLDriver seems a better approach to me.

Regards,
Davor