@MrBolton
Thanks for replying.

Your solution is not what I am looking for, unfortunately. I do not even have a QSortFilterProxyModel. Specifically, I do not want sorting to happen at the client. I wish it to happen at the server with a ORDER BY. My problem, IIRC, is that

QTableView::setSortingEnabled(true); QTableView::sortByColumn(col, Qt.DescendingOrder);

causes two SQL queries to be sent to the database, one for each line. Reversing the order of the two lines does not help. According to me, it is therefore not possible to enable sorting and pick which column to sort by without executing two queries in a row, which is ridiculously wasteful since we only care about the result of the second query. Users may not even be aware that this is what is happening behind the scenes. There should surely be some way of enabling sorting and specifying the column+direction without issuing two separate queries to the database. Nobody else but me seems to think this is an issue/bad/wrong!

I realise this question is now OT. If you would care to share your help on this matter please be kind enough to post in my original thread, https://forum.qt.io/topic/83294/how-to-prevent-qtableview-qtreeview-doing-query-sorting-multiple-times. Thank you.

I created custom model which works fast enough. It fetches and writes data using queries. Seems like working solution.

I got it done by the below code

QFileInfoList filelistinfo = dir.entryInfoList(); for(const QFileInfo &fileinfo: filelistinfo) imagePath.push_back(fileinfo.absoluteFilePath()); std::sort(imagePath.begin(), imagePath.end(), [](const QString & a, const QString & b) -> bool { return QFileInfo(a).baseName().toInt() < QFileInfo(b).baseName().toInt(); }); qDebug()<<imagePath;

You could set default sorting column to -1 by QHeaderView::setSortIndicator like this

yourTableView->horizontalHeader()->setSortIndicator(-1, Qt::AscendingOrder);

before running

yourTableView->setSortingEnabled(true);

because QTableView::setSortingEnabled uses QHeaderView::sortIndicatorOrder and QHeaderView::sortIndicatorSection to identify by which column should model be sorted.

Note that documentation of QHeaderView::setSortIndicator tells that not all models support setting sort column to -1 and may even crash in this case.

@MrBolton
Sorry, I really don't understand your comment. Precisely the point is that with "bigger data sets" you would have to fetch all the data, which is incredibly slow and may well exceed available memory. (OTOH, if the dataset is "small" the overhead of re-query compared to holding all the previous rows locally is also "small".) As a rule of thumb, one always wants as much work to be done at the server side as possible, not client side.

Let's say the table has a million rows and the query I want to pose is:

SELECT * FROM table ORDER BY column LIMIT 100

Very approximately, pushing the ORDER BY to the server instead of into a QSortFilterProxyModel will run 10 thousand times faster and use one ten-thousandth of the client memory. That's why I would be very careful before advising people to use QSortFilterProxyModel without understanding the ramifications!

Put a QSortFilterProxy model in-between. then save from the proxy instead of the main model.

P.S.
connect(currentTableHeader, SIGNAL(sectionClicked(int)), this, SLOT(on_sectionClicked(int))); and void mainWidget::on_sectionClicked(int index) are useless. this is the default behaviour of QTableView, you don't have to implement it manually

The solution was to explicitly call sort after the call to invalidate with setSortingEnabled set to false. Both invalidate and sort were necessary

@Lorence now its working, i dont know what happens yesterday

As a first go I tried the suggestion by @SGaist, which turned out to do exactly what I need for now. We're writing a lot from scratch, so for the future I'll certainly keep the idea of @kshegunov in mind, since it sounds a bit more flexible, so it may be required to support more advanced use cases coming our way in the (near) future.

Thanx to both!

@alex_malyu
i will add unique id to every group and add group to QStringList so that i can get a order childGroup.

Sort the tree view by click a column.

Set the view can be sorted by click the "header".

treeView_->setSortingEnabled(true);

Connect the header signal to a slot made by you.

connect(treeView_->header(), SIGNAL(sortIndicatorChanged(int, Qt::SortOrder)), treeModel_, SLOT(sortByColumn(int, Qt::SortOrder)));

In the slot, call the sort() virtual function of the model. sort() virtual function is a virtual function of QAbstractItemModel, and one should override it.

void TreeModel::sortByColumn(int column, Qt::SortOrder order) { sort(column, order); }

Override the sort() function as your model should do.

emit dataChanged(QModelIndex(), QModelIndex());from a model to update the whole tree view.