Drawing plots from sql data using datetime

[RogerWilco77]

Good afternoon,

I am facing a similar situation.
A database of power consumption readings.
Basically it consists of two tables (one with different meters and one with readings).

I have just installed qwt 6.1rc2 because it seems to have some useful features for this.

Actually the code (not elegant but ok for a beginner, I hope) works and gives me a graph.
Unfortunately the x-axis is totally cryptic. I am still struggling with QwtDateScaleEngine and QwtDateScaleDraw.

However, maybe the first part helps and maybe somebody gives me a hint about the usage of the scale engine and scale draw:

model = new QSqlRelationalTableModel;
    model->setTable("tbl_zaehlerstaende");                                                      // table with meter readings      
    model->setRelation(2, QSqlRelation("tbl_zaehler", "zaehler_ID", "name"));    //QSqlRelationalTableModel to link the two tables
    model->setFilter("name = 'my_meter'");                                                      //show only my own consumption
    model->sort(1, Qt::AscendingOrder);                                                          //sort in chronological order
    model->select();
 
    ui->tv_overview->setModel(model);
    ui->tv_overview->setItemDelegate(new QSqlRelationalDelegate(ui->tv_overview));
    ui->tv_overview->show();
 
 
 
 
int k = model->rowCount();                          //number of datapoints, ie readings
        QVector<QPointF> datapoints;
 
 
 
 
        for (int i = 0; i < k; i++)
        {
 
            QDateTime date;                                                             //the format in MySql is actually just DATE, but it does not seem to matter
            date = (model->data(model->index(i,1))).toDateTime();
 
            qreal x;
 
            x = QwtDate::toDouble(date);                                           //qwt needs a double to work
 
 
 
            datapoints.append(QPointF(x, qreal(model->data(model->index(i,3)).toInt())));
 
        }
 
            QwtPlotCurve *curve = new QwtPlotCurve();
 
            curve->setSamples(datapoints);
            curve->attach(ui->qwt_plot);
 
            ui->qwt_plot->replot();

model = new QSqlRelationalTableModel;
    model->setTable("tbl_zaehlerstaende");                                                      // table with meter readings      
    model->setRelation(2, QSqlRelation("tbl_zaehler", "zaehler_ID", "name"));    //QSqlRelationalTableModel to link the two tables
    model->setFilter("name = 'my_meter'");                                                      //show only my own consumption
    model->sort(1, Qt::AscendingOrder);                                                          //sort in chronological order
    model->select();

    ui->tv_overview->setModel(model);
    ui->tv_overview->setItemDelegate(new QSqlRelationalDelegate(ui->tv_overview));
    ui->tv_overview->show();




int k = model->rowCount();                          //number of datapoints, ie readings
        QVector<QPointF> datapoints;




        for (int i = 0; i < k; i++)
        {

            QDateTime date;                                                             //the format in MySql is actually just DATE, but it does not seem to matter
            date = (model->data(model->index(i,1))).toDateTime();

            qreal x;

            x = QwtDate::toDouble(date);                                           //qwt needs a double to work



            datapoints.append(QPointF(x, qreal(model->data(model->index(i,3)).toInt())));

        }

            QwtPlotCurve *curve = new QwtPlotCurve();

            curve->setSamples(datapoints);
            curve->attach(ui->qwt_plot);

            ui->qwt_plot->replot();

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Really I used google, I read the documentation. But I find it hard to get started.

Many greetings,

RogerWilco