use a combobox selection for linq query - wpf

Question

I have a combobox that gets populated from a database table. When the combobox is diplayed in the window it has the StationName, but it also has a "hidden" value for a StationId. Here is how I get the combobox to display the choices:
StationBox.ItemsSource = dc.WasteTrackerStations;
How can I get to that StationId property to use that in a seperate query to populate a datagrid? This is the code for my SelectionChanged event:
private void StationBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var miquery = from mi in dc.WasteTrackerDBs
where mi.StationId == [this value needs to be StationId from combobox selection]
select new
{
mi.MenuItem,
mi.LeftOver,
mi.Par,
mi.UoM,
mi.StationId
};
EWDataGrid.ItemsSource = miquery;
}

Answer 1

ComboBox has SelectedItem property. It will be an element of dc.WasteTrackerStations collection (or null). Cast it to concrete type and all properties will be accessible:
private void StationBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var item = StationBox.SelectedItem as WasteTrackerStation;
if (item == null) return;
var selectedStationId = item.StationId;
var miquery = from mi in dc.WasteTrackerDBs
where mi.StationId == selectedStationId
select new
{
mi.MenuItem,
mi.LeftOver,
mi.Par,
mi.UoM,
mi.StationId
};
EWDataGrid.ItemsSource = miquery;
}