public GroupTraineesByTester()
{
InitializeComponent();
bl = BL.FactoryBL.GetBL();
foreach (BE.Trainee item in bl.getTraineeList())
{
(item.NameOfTeacher) = bl.getTraineeTeacher(item.NameOfTeacher);
}
this.dataGrid.ItemsSource = bl.getTraineeList();
ListCollectionView collection = new ListCollectionView(bl.getTraineeList());
collection.GroupDescriptions.Add(new PropertyGroupDescription("NameOfTeacher"));
dataGrid.ItemsSource = collection;
}