QDataWidgetMapper and QSqlQueryModel

[cyberduck]

Hello,

how can i display some values from my database and write it back?

That is my QSqlQueryModel

QSqlQueryModel *model = new QSqlQueryModel();
model->setQuery("SELECT * FROM Experiment"
	"INNER JOIN Temperatur ON Experiment.ExperimentID = Temperatur.ExperimentID"
	"INNER JOIN Qualities ON Experiment.ExperimentID = Qualities.ExperimentID");

QSqlQueryModel *model = new QSqlQueryModel();
model->setQuery("SELECT * FROM Experiment"
	"INNER JOIN Temperatur ON Experiment.ExperimentID = Temperatur.ExperimentID"
	"INNER JOIN Qualities ON Experiment.ExperimentID = Qualities.ExperimentID");

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I set the model to a QDataWidgetMapper and add mapping for my QSliders

QDataWidgetMapper *mapper = new QDataWidgetMapper(this);
mapper->setModel(model);
mapper->setItemDelegate(new QSqlRelationalDelegate(this));
mapper->addMapping(ui.qslider_min, model->record(int_row)->indexOf("min"));
mapper->addMapping(ui.qslider_max, model->record(int_row)->indexOf("max"));
mapper->toFirst();

QDataWidgetMapper *mapper = new QDataWidgetMapper(this);
mapper->setModel(model);
mapper->setItemDelegate(new QSqlRelationalDelegate(this));
mapper->addMapping(ui.qslider_min, model->record(int_row)->indexOf("min"));
mapper->addMapping(ui.qslider_max, model->record(int_row)->indexOf("max"));
mapper->toFirst();

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The submit fails every time

mapper->submit();

mapper->submit();

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How can i write back the slider-values to my database? Can you help me please?

Thanks in Advance