Well, my answers:

  1. Qt Code: 
    1. QList<CMerchandizeOrder*> orders=shoppingCartModel()->orders();
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    gets full ist of previous orders in model, so I can check if processed order is already in list of orders so I can then update quantity (+1) and subtotal of order (recalculate quantity*price=subtotal)
  2. query.next() is executesd excalty ONCE
  3. here is addEntry code:
    Qt Code: 
    1. void CShoppingCartWidget::addEntry(structOrder& order)
    2. {
    3.     // debug block
    4.     qDebug() << "order.iMerchandizeID=" << order.iMerchandizeID;
    5.     qDebug() << "order.iMerchandizeQuantity=" << order.iMerchandizeQuantity;
    6.     qDebug() << "order.rMerchandizePrice=" << order.rMerchandizePrice;
    7.     qDebug() << "order.rSubtotal=" << order.rSubtotal;
    8.     qDebug() << "order.strDisplayString=" << order.strDisplayString;
    9.     qDebug() << "order.strMerchandizeName=" << order.strMerchandizeName;
    10.     // **** END of debug block
    11.  
    12.     QList<CMerchandizeOrder*> orders=shoppingCartModel()->orders();
    13.     CMerchandizeOrder* tempOrder=new CMerchandizeOrder(order);
    14.     Q_CHECK_PTR(tempOrder);
    15.  
    16. /*
    17.     tempOrder.iMerchandizeID=order.iMerchandizeID;
    18.     tempOrder.iMerchandizeQuantity=order.iMerchandizeQuantity;
    19.     tempOrder.rMerchandizePrice=order.rMerchandizePrice;
    20.     tempOrder.rSubtotal=order.rSubtotal;
    21.     tempOrder.strDisplayString=order.strDisplayString;
    22.     tempOrder.strMerchandizeName=order.strMerchandizeName;
    23. */
    24.  
    25.     if (!orders.contains(tempOrder))
    26.     {
    27.         // new merchandize
    28.         shoppingCartModel()->insertRows(0, 1, QModelIndex());
    29.         QModelIndex index=shoppingCartModel()->index(0, 0, QModelIndex());
    30.         shoppingCartModel()->setData(index,
    31.                                      //tempOrder.orderValues().strDisplayString,
    32.                                      tempOrder->orderValues().strDisplayString,
    33.                                      Qt::EditRole);
    34.     } 
    35.     else
    36.     {
    37.         // merchandize exists, update quantity and subtotal
    38.     }
    39. }
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So, I was working on the base of qt 4.4.0 example and there the object is created in same fashion like in my module ...