private void NewCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            var item = treeView.SelectedItem;

            if (item is DataAccess.Table)
            {
                var   popup = new NewStack(((DataAccess.Table)item).TableID);
                Stack stack;
                if (popup.ShowDialog().GetValueOrDefault())
                {
                    stack = popup.Stack;
                }
                else
                {
                    return;
                }
                using (var db = new NotesContext())
                {
                    db.Stacks.Add(stack);
                    db.SaveChanges();
                }
                treeView.Items.Refresh();
                treeView.UpdateLayout();
            }
        }
        private void NewCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            var item = treeView.SelectedItem;

            if (item is DataAccess.Table)
            {
                var   popup = new NewTable();
                Table table;
                if (popup.ShowDialog().GetValueOrDefault())
                {
                    table = popup.Table;
                }
                else
                {
                    return;
                }
                _context.Tables.Add(table);
            }
            else if (item is DataAccess.Stack)
            {
                var   popup = new NewStack(((DataAccess.Stack)item).TableID);
                Stack stack;
                if (popup.ShowDialog().GetValueOrDefault())
                {
                    stack = popup.Stack;
                }
                else
                {
                    return;
                }
                ((DataAccess.Stack)item).Table.Stacks.Add(stack);
                //_context.Stacks.Add(stack);
            }
            else if (item is DataAccess.Book)
            {
                var  popup = new NewBook(((DataAccess.Book)item).StackID);
                Book book;
                if (popup.ShowDialog().GetValueOrDefault())
                {
                    book = popup.Book;
                }
                else
                {
                    return;
                }
                ((DataAccess.Book)item).Stack.Books.Add(book);
            }

            _context.SaveChanges();

            treeView.Items.Refresh();
            treeView.UpdateLayout();
        }