How to sort original data structure of QAbstractTableModel?

[CuriousPan]

Hello!
I'm using QAbstractTableModel for representing data in table. Also, I'm using QSortFilterProxyModel as a wrapper for sorting. Hence, I implement lessThan method for comparison.
Unfortunately, this sorts only the view, but I also need to sort the data structre my table takes data from. Is there a way to do it?

[eyllanesc]

@CuriousPan Qt doesn't do that but if you want to implement that feature then override the model's QAbstractItemModel::sort method and implement the sorting there.

[CuriousPan]

@eyllanesc, well, I implemented sort method in QAbstractTableModel, but it's not even called.

[eyllanesc]

@CuriousPan How are they calling him or what action should he be called upon? You should no longer use QSortFilterProxyModel.

[JonB]

@CuriousPan said in How to sort original data structure of QAbstractTableModel?:

well, I implemented sort method in QAbstractTableModel, but it's not even called.

You have to call it if you want it to sort.

Also, I'm using QSortFilterProxyModel as a wrapper for sorting.
[...]
Unfortunately, this sorts only the view,

No "view" involved here. QSortFilterProxyModel is a proxy for your model, it's a model itself. You have to access via the proxy model if you want to see things sorted, it does not sort the underlying model.

[CuriousPan]

@JonB, now I'm calling sort method of source model in lessThan method. The datastructre is getting sorted, as well as the view, but view is sorted incorrectly. Isn't it strange?
Here's the view:

Printout of the situation inside the datastructure:

[JonB]

@CuriousPan said in How to sort original data structure of QAbstractTableModel?:

now I'm calling sort method of source model in lessThan method.

Pardon? That is not going to be a good thing to do....

but view is sorted incorrectly.

Now I'm not sure whether your view is connected to your QSortFilterProxyModel or your underlying (sorted) model.

You had better show code --- preferably minimal --- for whatever you are doing which illustrates problem.

P.S.
If you are really calling a sort() inside a lessThan() comparison, and that changes the order of the data, your results e.g. in a view are liable to be rubbish. You must not do that! Any lessThan() method will be const, and you should regard it as forbidden to change any state inside it.

[CuriousPan]

Okay, here's the code:

//m_model is a ForecastingProxyModel class inheriting from QAbstractTableModel
ForecastingProxyModel *proxyModel = new ForecastingProxyModel(this);
proxyModel->setSourceModel(m_model);
ui->forecastingTableView->setModel(proxyModel);
ui->forecastingTableView->setSortingEnabled(true);

Here's the code of the lessThan of the QSortFilterProxyModel:

bool ForecastingProxyModel::lessThan(const QModelIndex &sourceLeft, const QModelIndex &sourceRight) const
{
    const QVariant &leftData = sourceModel()->data(sourceLeft);
    const QVariant &rightData = sourceModel()->data(sourceRight);
    //sourceModel()->sort(sourceLeft.column(), sortOrder());  you said it's a bad idea to call it hear.

    if (leftData.userType() == QMetaType::QDate) {
        return leftData.toDate() < rightData.toDate();
    } else if (leftData.userType() == QMetaType::QString) {
        return leftData.toString() < rightData.toString();
    } else if (leftData.userType() == QMetaType::Double) {
        return leftData.toDouble()  < rightData.toDouble();
    } else if (leftData.userType() == QMetaType::Bool) {
        return leftData.toBool() < rightData.toBool();
    }

    return QSortFilterProxyModel::lessThan(sourceLeft, sourceRight);
}

Here's a sort method of the source model:

void ForecastingModel::sort(int column, Qt::SortOrder order)
{
    switch(column) {
    case Name:
        if (order == Qt::AscendingOrder) {
            std::sort(m_logicController->forecasts().begin(), m_logicController->forecasts().end(),
                      [](const Forecast &a, const Forecast &b) { return a.name < b.name; });
        } else {
            std::sort(m_logicController->forecasts().begin(), m_logicController->forecasts().end(),
                      [](const Forecast &a, const Forecast &b) { return a.name > b.name; });
        }
        break;

    case Price:
        if (order == Qt::AscendingOrder) {
            std::sort(m_logicController->forecasts().begin(), m_logicController->forecasts().end(),
                      [](const Forecast &a, const Forecast &b) { return a.price < b.price; });
        } else {
            std::sort(m_logicController->forecasts().begin(), m_logicController->forecasts().end(),
                      [](const Forecast &a, const Forecast &b) { return a.price > b.price; });
        }
        break;
    }
}

Is it enough or something more is required?

[JonB]

@CuriousPan
Well, you certainly do not want to have called sourceModel()->sort() inside ForecastingProxyModel::lessThan(), so that's an improvement!

You don't call (or show you have called) your ForecastingModel::sort(), so I think that is irrelevant.

Then your view is attached to your QSortFilterProxyModel. I would start by debugging/printing from within lessThan() to see which column is in the QModelIndexes to compare so you know what it is sorting by, and maybe check the values. I don't think your "Printout of the situation inside the datastructure:" is relevant because you are accessing via the QSortFilterProxyModel, so the ordering comes from there.

While I think of it: I don't think your lessThan() handles any QVariant types not already catered for in https://doc.qt.io/qt-5/qsortfilterproxymodel.html#lessThan (except maybe Bool, but that probably degenerates correctly anyway, or isn't relevant to your data), so don't think your lessThan() does anything which is actually needed?

[CuriousPan]

@JonB,
After suggested debugging I found out following things:

1. lessThan method considers Date as String, which I find quite suprising. I can fix it by checking the data behind QModelIndex using not QMetaType, but rather column number.
2. lessThan doesn't recognize bool type too.
3. lessThan considers columns correctly.

While I think of it: I don't think your lessThan() handles any QVariant types not already catered for in https://doc.qt.io/qt-5/qsortfilterproxymodel.html#lessThan (except maybe Bool, but that probably degenerates correctly anyway, or isn't relevant to your data), so don't think your lessThan() does anything which is actually needed?

What do you exactly mean by this?

You don't call (or show you have called) your ForecastingModel::sort(), so I think that is irrelevant.

Where am I supposed to call it? Isn't it a slot wihich is called autimatically?

[Christian Ehrlicher]

@CuriousPan said in How to sort original data structure of QAbstractTableModel?:

bool ForecastingProxyModel::lessThan(const QModelIndex &sourceLeft, const QModelIndex &sourceRight) const
{
const QVariant &leftData = sourceModel()->data(sourceLeft);
const QVariant &rightData = sourceModel()->data(sourceRight);
//sourceModel()->sort(sourceLeft.column(), sortOrder()); you said it's a bad idea to call it hear.

if (leftData.userType() == QMetaType::QDate) {
    return leftData.toDate() < rightData.toDate();
} else if (leftData.userType() == QMetaType::QString) {
    return leftData.toString() < rightData.toString();
} else if (leftData.userType() == QMetaType::Double) {
    return leftData.toDouble()  < rightData.toDouble();
} else if (leftData.userType() == QMetaType::Bool) {
    return leftData.toBool() < rightData.toBool();
}

return QSortFilterProxyModel::lessThan(sourceLeft, sourceRight);

This is not needed. QSortFilterProxyModel does exact the same (and honors more meta types than your implementation)

[CuriousPan]

@Christian-Ehrlicher, do you suggest totally removing the method?

[JonB]

@CuriousPan
If you followed my link it lists:

This function is used as the < operator when sorting, and handles the following QVariant types:

So you see how it says which QVariant types it handles and that includes the ones you handle. It also includes QMetaType::QDate so I don't know why your "lessThan method considers Date as String, which I find quite suprising". I don't believe you need your own override.

EDIT I can see @Christian-Ehrlicher agrees.

Put qDebug() statements inside your sort() to see whether it's called. Your view is attached to the QSortFilterProxyModel rather than the underlying model. I'm not sure, but find out which models' sorting are getting used/called. I don't think QSortFilterProxyModel::sort() will call sourceModel->sort(). I think it's confusing to have sorting on your source model and also to be using QSortFilterProxyModel against it.

Where am I supposed to call it?

I would normally expect you to sort a (source) model immediately after you populate it if you want it sorted. So wherever that is in your code.

[CuriousPan]

After removing lessThan method I have following behavior:

1. QSortFilterProxyModel::sort() is getting called, but not the source one, hence I have to call source::sort() inside it. It sorts source data, but view isn't changing.

[JonB]

@CuriousPan
I have said before: I do not know why you are using a QSortFilterProxyModel and also doing sourceModel()->sort(). If you want to sort the underlying model I don't know why you want the proxy too. But there you are.

Meanwhile, since again you do not show your code for "hence I have to call source::sort() inside it", we do not know what you are doing. Are you/do you need to take QSortFilterProxyModel::sortColumn() & QSortFilterProxyModel::sortOrder() into account?

It sorts source data, but view isn't changing.

I have said before: the view is bound to the QSortFilterProxyModel, not the source model directly, so I don't know that any change you might or might not make in the source model's rows' order would be reflected in either the QSortFilterProxyModel or any view bound to it.

I would get it working with either the QSortFilterProxyModel and no source model sort() or source model sort() and no QSortFilterProxyModel --- and possibly compare the two --- before I tried to understand what was happening with both in play.

That's all I know to say.

[CuriousPan]

After searching the internet I guess I found a solution. After sorting the data it's important to emit dataChanged.
Thanks everyone who tried to help me.

[JonB]

@CuriousPan
That is a good point, which I should have thought about! :)

I still don't know why you want both to sort the model and to have a sort proxy on top of it. You sure you want the QSortFilterProxyModel at all, given your desire to sort the underlying model? Best of luck.

[Christian Ehrlicher]

@JonB said in How to sort original data structure of QAbstractTableModel?:

I still don't know why you want both to sort the model and to have a sort proxy on top of it.

Because he does not understand what a QSortFilterProxyModel is doing...

[CuriousPan]

@Christian-Ehrlicher, yeah, you are right. I was given the example with QSortFilterProxyModel so I thought it's mandatory to use it. I've removed it.

[Christian Ehrlicher]

Sorting the base model is normally much more expansive than using a QSortFilterProxyModel so it should be avoided.