Export QTableView data with a delegated column to CSV

JonB

QVariant MyModel::data(const QModelIndex &index, int role /*= Qt::DisplayRole*/) const
{
    if (!index.isValid())
        return QVariant();
    QVariant v = BaseModel::data(index, role);
    if (role == Qt::DisplayRole)
        if (isTimeStampColumn(index.column()))
        {
            double value = v.toDouble();
            ...
            return QDateTime::fromMSecsSinceEpoch(qd_ts, Qt::LocalTime).toString("yyyy-MM-dd HH:mm:ss.zzz");
        }
    return v;
}

If you want to correctly sort on this column, you ought have a sort role which returns the base data value, not the string.

Remember from what I said above, don't blame me if one of the expert critics --- @VRonin, IIRC, though I might be mistaken --- calls for your beheading for using this approach... ;-)

VRonin

What I would do:
In the delegate, don't reimplement paint(), but displayText() (it's also a lot easier than what you did):

 class TimeDgDelegate : public QStyledItemDelegate{
Q_OBJECT
public:
using QStyledItemDelegate::QStyledItemDelegate;
QString displayText(const QVariant &value, const QLocale &locale) const override{
double value = value.toDouble();
double qd_ts = value*1.25/(256.0*256.0);
qd_ts += 315964800000;
return locale.toString(QDateTime::fromMSecsSinceEpoch(qd_ts, Qt::LocalTime),QStringLiteral("yyyy-MM-dd HH:mm:ss.zzz"));
}
};

Then your csv export would become:

for (int i = 0; i < rows; i++) {
    for (int j = 0; j < columns; j++) {
        const QModelIndex idx = model->index(i,j);
        textData += ui->tableView->itemDelegate(idx)->displayText(model->data(idx),locale()) + QLatin1Char(',');
    }
    textData += QLatin1Char('\n'); 
}

P.S.
Probably doesn't apply here but generally csv exporting requires you to escape , and " characters in the data

morteza ali ahmadi

@JonB Thank you again for your codes.

JonB

@VRonin
Thanks for posting. I forget about just QStyledItemDelegate::displayText(), that's a good one to remember.

Assuming you are indeed the expert poster in the past about use of Qt::DisplayRole I recall, and who called for my execution :) You don't like that use of the model/display role, and now I feel similarly uncomfortable about your use of anything QStyledItemDelegate, ui->tableView->itemDelegate(idx), when you are exporting model data to CSV. Your export requires access to a UI table view, but the format for CSV export has nothing to do with any model views, and there is no reason to suppose exporting code would have any UI access at all, or even be a GUI application. IMHO. We're probably not going to agree ;-)

morteza ali ahmadi

@VRonin Thank you very much, yes, it could solve my problem with a better implementation.

VRonin

@JonB said in Export QTableView data with a delegated column to CSV:

Your export requires access to a UI table view, but the format for CSV export has nothing to do with any model views, and there is no reason to suppose exporting code would have any UI access at all, or even be a GUI application

I think we actually agree on this one. The clean way here is to have a function that handles the conversion of data from double to QDate. The delegate will call it and then format it as a string to display, the csv serialiser will call it and then save the QDate to csv.

Assuming you are indeed the expert poster in the past about use of Qt::DisplayRole I recall, and who called for my execution

This is a very corner case in which your approach doesn't do much harm and can be used. if, however, the date format was dd-MM-yyyy HH:mm:ss.zzz then your solution would break sorting in the table (as it would sort as string, not as dates)

JonB

@VRonin said in Export QTableView data with a delegated column to CSV:

I think we actually agree on this one.

Amazing :)

This is a very corner case in which your approach doesn't do much harm

It is good to know that at worst I am "harmless" ;-)

The clean way here is to have a function that handles the conversion of data from double to QDate. The delegate will call it and then format it as a string to display, the csv serialiser will call it and then save the QDate to csv.

I suggested that as my 3rd alternative.

then your solution would break sorting in the table (as it would sort as string, not as dates)

Absolutely, and I thought I typed into my answer about if you did this you need to use a different sort role if you sort, but maybe I deleted that. But yes people should bear this in mind.

morteza ali ahmadi

@VRonin Does your solution convert epochs format to string one twice? i.e. for each database record in your solution,

Conversion with displayText function is used to display "yyyy-MM-dd HH:mm:ss.zzz" format in QTableView and,
Conversion with displayText function is used to store "yyyy-MM-dd HH:mm:ss.zzz" format in CSV.

Is it right?

VRonin

correct, you are basically using displayText as a fancy toString().

Also, just to be clear, the delegate repaints on demand and doesn't cache the displayText so it's actually calculated every time a repaints happens

morteza ali ahmadi

@VRonin, So I think the combination of your solution and the third solution of @JonB is the best choice. It means that, I can override displayText() instead of paint() and use a function X within that which handles the conversion of data from double to "dd-MM-yyyy HH:mm:ss.zzz". Also, the X function can be used in export to CSV procedure.

@VRonin and @JonB, do you agree with me?

JonB

@morteza-ali-ahmadi Yes.

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