Hi ~~ i loaded data using this code void benefits::on_monthvbutton_clicked() { counters = 0; QSqlQuery qry(db); qry.prepare("SELECT * FROM fac WHERE month= '"+ui->monthdateedit->text()+"'"); if(qry.exec("SELECT * FROM fac WHERE month= '"+ui->monthdateedit->text()+"'")){ qDebug()<<"yep works"; while(qry.next()){ counters +=qry.value(9).toFloat(); } }else{ // ui->statusfacture->setText(qry.lastError().text()); } if(counters==NULL){ ui->benefitmonthtextedit->setText(QString("")); }else{ ui->benefitmonthtextedit->setText(QString("you have %1 as benefits this month ").append("dollars Canadian").arg(counters)); } } it works fast as i want .. but the problem is i don't know how to make it work on another thread may be someday it needs to calculate 10000 rows per month .. so it will freeze The Main Thread and GUI... i tried everything .. can someone help me on this?

@ Proton-Phoenix said in loading data from database using another thread : here it says you can't run Widgets on another thread ... i understand that but i didn't find in the internet how to load just data on another thread i will try to search more on the basics Thank you so much bro for help The easiest way is to use QtConcurrent::run() in combination with QFutureWatcher : For example: void benefits::on_monthvbutton_clicked() { QSqlQuery qry(db); qry.prepare("SELECT * FROM fac WHERE month=:data"; query.bindValue(":data", ui->monthdateedit->text()); if(qry.exec()) { qDebug()<<"yep works"; // watcher to wait until future is done auto watcher = new QFutureWatcher<float>(); // ==> delete QFuteWatcher instance instance when process done connect(watcher, &QFutureWatcher<float>::finished, watcher, [watcher, this]() { qDebug() << "Processing done."; float counters = watcher->result(); watcher->deleteLater(); if(!counters){ ui->benefitmonthtextedit->setText(QString("")); }else{ ui->benefitmonthtextedit->setText(QString("you have %1 as benefits this month dollars Canadian").arg(counters)); } }); // start processing in another thread QFuture<float> future = QtConcurrent::run([qry]() ->float { // Code in this block will run in another thread qDebug() << "Processing in another thread"; float counters = 0; int colCounter = query.record().indexOf("counter"); // I suppose column name is counter while(qry.next()){ counters +=qry.value(colCounter).toFloat(); } return counters; }); watcher->setFuture(future); }else{ //ui->statusfacture->setText(qry.lastError().text()); } }

@ Proton-Phoenix said in loading data from database using another thread : it works fast as i want .. but the problem is i don't know how to make it work on another thread may be someday it needs to calculate 10000 rows per month .. so it will freeze The Main Thread and GUI... i tried everything .. can someone help me on this? Your code looks a little bit confusing: why do you do qry.prepare(...) and then qry.exec(...) with the same string? you can remove qry.prepare using qry.value(9).toFloat() with SELECT * FROM ... is not really appropriated. I recommend you to change this to ensure you will get the value you want. and if(counters==NULL) should be if(counters==0) or if(!counters) I would change this to: void benefits::on_monthvbutton_clicked() { counters = 0; QSqlQuery qry(db); qry.prepare("SELECT * FROM fac WHERE month=:data"; qry.bindValue(":data", ui->monthdateedit->text()); if(qry.exec()) { qDebug()<<"yep works"; int colCounter = query.record().indexOf("counter"); // I suppose column name is counter while(qry.next()){ counters +=qry.value(colCounter).toFloat(); } }else{ //ui->statusfacture->setText(qry.lastError().text()); } if(counters==0){ ui->benefitmonthtextedit->setText(QString("")); }else{ ui->benefitmonthtextedit->setText(QString("you have %1 as benefits this month dollars Canadian").arg(counters)); } }

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loading data from database using another thread

Solved General and Desktop

21 Posts 3 Posters 2.9k Views

C Christian Ehrlicher

@KroMignon Or do only the calculation in the other thread.
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Proton Phoenix

wrote on last edited by Proton Phoenix

#21

@Christian-Ehrlicher and @KroMignon
i did it successfully Thanks you so much your opinions helped me to fix the Big O problem too
now it's only calculation with the other thread
<3
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