Question

So here is the situation. I am using ADP.NET Data Services 1.5 CTP2 with Silverlight 3. My EF data model is (in short) like this:

CmsProfile
      Id
      Name

CmsEvent
      Id
      Title

CmsProfileEventLink
      Id
      ProfileId
      EventId

So there is a many <-> many relationship between people and events. When I load the events within silverlight, I do it this way:

private void AsyncLoadEventsKickoff()
{
    DataServiceQuery<CmsEvent> theQuery = dashboardService
        .CmsEvents
        .Expand("CmsProfileEventLinks")
        .AddQueryOption("$orderby", "Title");

    theQuery.BeginExecute(
        delegate(IAsyncResult asyncResult)
        {
            Dispatcher.BeginInvoke(
                () =>
                {
                    DataServiceQuery<CmsEvent> query = 
                        asyncResult.AsyncState as DataServiceQuery<CmsEvent>;
                    if (query != null)
                    {
                        //create a tracked DataServiceCollection from the 
                        //result of the asynchronous query.
                        events = DataServiceCollection
                            .CreateTracked<CmsEvent>(dashboardService,
                                query.EndExecute(asyncResult));

                        AsyncLoadTracker();
                    }
                }
            );
        },
        theQuery
    );
}

You will notice that I cannot get Expand() to actually drop the next level and get me the event link details. It will only really tell me if there ARE event link records or not.

I put all the events into a grid (SelectionGrid), and when you click one, I want to load ANOTHER grid (EventsGrid) with the people that are related to this event. I do this by loading the grid with CmsProfileEventLink objects and then drilling down on the DataMemberPath to the profile name. In theory, this allows the grid to add new links for me – when a row is added I give it an Id, and set the CmsEvent to the current event, take the user input for the Profile and blammo – new linked record.

In a perfect world I could just set peopleGrid.ItemsSource = EventsGrid.Selecteditem.CmsPeopleEventLinks and the whole thing would work as expected. However since the expansion doesn’t got that deep, I can’t.

As a workaround I have loaded all the CmsProfileEventLinks the same way into a “links” variable. So when you select a event I do this (ugly, ugly, ugly) to show the profiles…

private void Sync_EventsGrid()
{
    var item = SelectionGrid.SelectedItem as CmsEvent;

    if (item.CmsEventProfileLinks != null)
    {
        DataServiceCollection<CmsEventProfileLink> x = 
            DataServiceCollection
                .CreateTracked<CmsEventProfileLink>(
                     dashboardService, 
                     links.Where(p => p.CmsEvent == item));

        EventsGrid.ItemsSource = x;
    }
}

The problem is… that if a change is made within EventsGrid it does NOT propagate back to links context, even though they both share a DataService context. The net result? if you select a different event and come back, the EventsGrid does NOT show the recently added record. If you refresh the application, forcing it to re-read links from the database? it picks it up.

So I need any of the following…

1. A way to do the 2 level expansion
   of the CmsEvent record on initial
   load so I can simply pass its links
   property to the second grid
   (preserving the context)

2. A better way to get a filtered
   view of “links” that does NOT spawn
   an independant context that doesnt
   update

3. A way to notify the “links”
   object that it should refresh,
   preferably without forcing it to go
   all the way back to the server via a
   async call – since the data clearly
   has been updated in the local
   context.

Any hints?

Answer 1

You could loop over the expanded property and call LoadProperty on each one to expand its children, like so:

DataServiceQuery<CmsEvent> query 
                         = asyncResult.AsyncState as DataServiceQuery<CmsEvent>;
if (query != null)
{
    //create a tracked DataServiceCollection from the 
    //result of the asynchronous query.
    events = DataServiceCollection.CreateTracked<CmsEvent>(dashboardService,
                                                 query.EndExecute(asyncResult));
    AsyncLoadTracker();

    foreach(var link in events.SelectMany(e=> e.CmsProfileEventLink))
    {
         dashboardService.LoadProperty(link, "CmsPeopleEventLinks");
    }
}