C# 4 and .NET 4

Using WCf Data services with the aDo.neT entity framework ❘ 899
To create a DataServiceCollection < T > instance the class DataServiceCollection defi nes the static
methods Create() and CreateTracked() . Create() creates a list that is independent of the data service
context. CreateTracked() keeps track of the objects returned from the data service context so that you can
take advantage of saving the objects by sending the changes to the service.
The Menus property invokes the DataServiceCollection.CreateTracked < T > () method to fi ll a
DataServiceCollection < R.Menu > list named t r a c k e d M e n u s and returns this list. The retrieved entities
that are defi ned by the LINQ query are associated with the data service context d at a .
public IEnumerable < R.Menu > Menus
{
get
{
if (trackedMenus == null)
trackedMenus = DataServiceCollection.CreateTracked < R.Menu > (
data,
from m in data.Menus
where m.CategoryId == (comboCategories.SelectedItem as R.Category).Id
& & m.Active
select m);
return trackedMenus;
}
}
code snippet ClientApp/MainWindow.xaml.cs
The DataGrid from the XAML code maps to the Menus property with the Binding markup extension:
< DataGrid Grid.Row="2" ItemsSource="{Binding Path=Menus}" AutoGenerateColumns="False" >
< DataGrid.Columns >
< DataGridTextColumn Binding="{Binding Path=Name}" / >
< DataGridTextColumn Binding="{Binding Path=Description}" / >
< DataGridTextColumn Binding="{Binding Path=Price}" / >
< DataGridTextColumn Binding="{Binding Path=CategoryId}" / >
< /DataGrid.Columns >
< /DataGrid >
code snippet ClientApp/MainWindow.xaml
Using the SelectionChanged event from the ComboBox to select a new category, the menus are retrieved
again with the newly selected category in the handler method OnCategorySelection() :
private void OnCategorySelection(object sender, SelectionChangedEventArgs e)
{
}
var selectedCategory = comboCategories.SelectedItem as R.Category;
if (selectedCategory != null & & trackedMenus != null)
{
trackedMenus.Clear();
trackedMenus.Load(from m in data.Menus
where m.CategoryId == selectedCategory.Id
select m);
}
code snippet ClientApp/MainWindow.xaml.cs
For more information about observable collections and the class ObservableCollection
please consult Chapter 10, “Collections.”
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