How can I create and use several connections to a SQL db in different threads in a Qt application?
I've read the documentation which says
A connection can only be used from within the thread that created it.
How can I separate connections in different threads?
You should create a database connection per thread. Use QSqlDatabase::addDatabase() with different connection names as parameters in each thread to create instances of QSqlDatabase. The static addDatabase function is thread safe and could be called in different threads.
QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL", __func__);How can I create and use several connection to sql db in a different threads in the program using Qt?
// general worker init slot
DbWorker::init()
{
this->db = QSqlDatabase::addDatabase("QSQLITE", dbName);
db.setDatabaseName(dbPath);
db.open();
}
when in your main class or wherever you have something like:
DbWorker w1 = new DbWorker;
w1.setDbName("mem_db");
w1.setDbPath(":memory:");
QThread* t1 = new QThread(this);
w1->moveToThread(t1);
connect(t1, SIGNAL(started()), w1, SLOT(init()));
t1->start();
DbWorker w2 = new DbWorker;
w1.setDbName("file_db");
w1.setDbPath("~/usr/foo.db");
QThread* t2 = new QThread(this);
w1->moveToThread(t1);
connect(t2, SIGNAL(started()), w2, SLOT(init()));
t1->start();
so you have your memory connection in thread1 and the file connection in thread2. the only thing to manage is to fetch data to the gui thread if it is a gui application
non gui threads are not allowed to access the gui elements. share your data with signals/slots and you should be good to goFollow this tutorial from VoidRealms @ youtube. He has a very good explanation on sql connection,models and many other stuff about Qt.
If you still need more help after watching it, it would be my pleasure to send you a sample code for you to test it.
