使用WCF RIA、Entity Framework 4、Silverlight 4进行惯用默认排序?

我有两个Silverlight4.0组合框;第二个组合框显示在第一个组合框中选择的实体的子项:

<ComboBox 
    Name="cmbThings"
    ItemsSource="{Binding Path=Things,Mode=TwoWay}"
    DisplayMemberPath="Name"
    SelectionChanged="CmbThingsSelectionChanged" />
<ComboBox 
    Name="cmbChildThings"
    ItemsSource="{Binding Path=SelectedThing.ChildThings,Mode=TwoWay}"
    DisplayMemberPath="Name" />

视图背后的代码提供了一种(简单的、黑客式的)数据绑定这些组合框的方法,方法是通过WCF RIA服务加载Entity Framework 4.0实体:

public EntitySet<Thing> Things { get; private set; }
public Thing SelectedThing { get; private set; }

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    var context = new SortingDomainContext();
    context.Load(context.GetThingsQuery());
    context.Load(context.GetChildThingsQuery());
    Things = context.Things;            
    DataContext = this;
}

private void CmbThingsSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    SelectedThing = (Thing) cmbThings.SelectedItem;
    if (PropertyChanged != null)
    {
        PropertyChanged.Invoke(this, new PropertyChangedEventArgs("SelectedThing"));
    }
}

public event PropertyChangedEventHandler PropertyChanged;

我想做的是让两个组合框按字母顺序对其内容排序,如果可能的话,我想在XAML中指定这种行为。

有人能告诉我使用SL4/EF4/WCF RIA技术栈的惯用方法是什么吗?