The role you need to use in QAbstractItemModel::data is Qt::CheckStateRole. I think the method should look like this:

Qt Code: 
  1. QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
  2. {
  3.     if (!index.isValid())
  4.     {
  5.         return QVariant();
  6.     }
  7.     QSqlRecord rec = record(index.row());
  8.     QVariant val = rec.value(index.column());
  9.  
  10.     switch (role)
  11.     {
  12.     case Qt::CheckStateRole:
  13.         if (index.column() != 6)
  14.             return QVariant();
  15.         else if (val.toInt() == 0) // or whatever
  16.             return Qt::Unchecked;
  17.         else
  18.             return Qt::Checked;
  19.     case Qt::DisplayRole:
  20.         return val;
  21.     default:
  22.         return QVariant();
  23.     }
  24. }
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Depending on the type stored in val, QVariant::toString() may well return an empty string. Use QVariant::typeName() to check what type it is. I think it's best to just pass on the QVariant value.

No guarantees, I did not check the code above, but I hope it gives you an idea.