relationalModel() pointer and segfault

[tranfuga25s]

Using qt4 with a QSqlRelationalTableModel, if I try to use one method of the relational model with:

MProductos *m = qobject_cast<MProductos *>(this->relationModel( 2 ));
flag = m->productoVendido( id, cant );

MProductos *m = qobject_cast<MProductos *>(this->relationModel( 2 ));
flag = m->productoVendido( id, cant );

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inside of the method productoVendido I get SegFault:

bool MProductos::productoVendido( QVariant id, QVariant cantidad )
{
 qDebug( "Actualizando stock por venta" );
 QModelIndex indice = index( id.toInt(), 6, QModelIndex() );  /// Here I get segfault
 if( !indice.isValid() )
 {
    qDebug( "Error de indice al intentar actualizar productos! - indice invalido" );
    return false;
 }
 QVariant cantAnterior = this->data( this->index( id.toInt(), 6 ), Qt::EditRole );
 QVariant cantActual = QVariant::fromValue( cantAnterior.toDouble() - cantidad.toDouble() );
 return this->setData( this->index( id.toInt(), 6 ), cantActual );
}

bool MProductos::productoVendido( QVariant id, QVariant cantidad )
{
 qDebug( "Actualizando stock por venta" );
 QModelIndex indice = index( id.toInt(), 6, QModelIndex() );  /// Here I get segfault
 if( !indice.isValid() )
 {
    qDebug( "Error de indice al intentar actualizar productos! - indice invalido" );
    return false;
 }
 QVariant cantAnterior = this->data( this->index( id.toInt(), 6 ), Qt::EditRole );
 QVariant cantActual = QVariant::fromValue( cantAnterior.toDouble() - cantidad.toDouble() );
 return this->setData( this->index( id.toInt(), 6 ), cantActual );
}

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It's correct the using that I geave to the pointer o shud I make a new instance of the model?

Thanks

[marcel]

Either 6 is an out of range column or id is not valid.
Could you see what id.isNull() and id.isValid() return?

Regards

[tranfuga25s]

No, I cant, because the program gets segfault in that exact point.
The column 6 exists, I've used it on the constructor of the model:

setHeaderData( 6, Qt::Horizontal, tr( "Stock" ) );

setHeaderData( 6, Qt::Horizontal, tr( "Stock" ) );

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and id, comes from the original model, I get it with:

QVariant id = QSqlTableModel::data( this->index( fila, 2 ) );

QVariant id = QSqlTableModel::data( this->index( fila, 2 ) );

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so, seems that the id it's valid.
Even I change the qobject_cast<.... with a "new" operator, still getting invalid index in every situation.

I'm using sqlite. May be that the problem, the method venderProducto( ... ) is called from inside another model. May be that i cant update that data because, the original model is locking the db??