Hey all, I have two functions in a SL project (VS2010) that do almost exactly the same thing, yet one throws an error and the other does not. It seems to be related to the projections, but I am unsure about the best way to resolve.

The function that works is...

public void LoadAllChunksExpandAll(DataHelperReturnHandler handler, string orderby)
    {
        DataServiceCollection<CmsChunk> data = null;

        DataServiceQuery<CmsChunk> theQuery = _dataservice
            .CmsChunks
            .Expand("CmsItemState")
            .AddQueryOption("$orderby", orderby);

        theQuery.BeginExecute(
            delegate(IAsyncResult asyncResult)
            {
                _callback_dispatcher.BeginInvoke(
                        () =>
                        {
                            try
                            {
                                DataServiceQuery<CmsChunk> query = asyncResult.AsyncState as DataServiceQuery<CmsChunk>;
                                if (query != null)
                                {
                                    //create a tracked DataServiceCollection from the result of the asynchronous query.
                                    QueryOperationResponse<CmsChunk> queryResponse =
                                        query.EndExecute(asyncResult) as QueryOperationResponse<CmsChunk>;
                                    data = new DataServiceCollection<CmsChunk>(queryResponse);

                                    handler(data);
                                }
                            }
                            catch
                            {
                                handler(data);
                            }
                        }
                    );
            },
            theQuery
        );
    }

This compiles and runs as expected. A very, very similar function (shown below) fails...

             public void LoadAllPagesExpandAll(DataHelperReturnHandler handler, string orderby)
    {
        DataServiceCollection<CmsPage> data = null;

        DataServiceQuery<CmsPage> theQuery = _dataservice
            .CmsPages
            .Expand("CmsChildPages")
            .Expand("CmsParentPage")
            .Expand("CmsItemState")
            .AddQueryOption("$orderby", orderby);

        theQuery.BeginExecute(
            delegate(IAsyncResult asyncResult)
            {
                _callback_dispatcher.BeginInvoke(
                        () =>
                        {
                            try
                            {
                                DataServiceQuery<CmsPage> query = asyncResult.AsyncState as DataServiceQuery<CmsPage>;
                                if (query != null)
                                {
                                    //create a tracked DataServiceCollection from the result of the asynchronous query.
                                    QueryOperationResponse<CmsPage> queryResponse = query.EndExecute(asyncResult) as QueryOperationResponse<CmsPage>;
                                    data = new DataServiceCollection<CmsPage>(queryResponse);

                                    handler(data);
                                }
                            }
                            catch
                            {
                                handler(data);
                            }
                        }
                    );
            },
            theQuery
        );
    }

Clearly the issue is the Expand projections that involve a self referencing relationship (pages can contain other pages). This is under SL4 or SL3 using ADONETDataServices SL3 Update CTP3.

I am open to any work around or pointers to goo information, a Google search for the error results in two hits, neither particularly helpful that I can decipher.

The short error is "An item could not be added to the collection. When items in a DataServiceCollection are tracked by the DataServiceContext, new items cannot be added before items have been loaded into the collection."

The full error is...

System.Reflection.TargetInvocationException was caught Message=Exception has been thrown by the target of an invocation. StackTrace: at System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters) at System.Data.Services.Client.ClientType.ClientProperty.SetValue(Object instance, Object value, String propertyName, Boolean allowAdd) at System.Data.Services.Client.AtomMaterializer.ApplyItemsToCollection(AtomEntry entry, ClientProperty property, IEnumerable items, Uri nextLink, ProjectionPlan continuationPlan) at System.Data.Services.Client.AtomMaterializer.ApplyFeedToCollection(AtomEntry entry, ClientProperty property, AtomFeed feed, Boolean includeLinks) at System.Data.Services.Client.AtomMaterializer.MaterializeResolvedEntry(AtomEntry entry, Boolean includeLinks) at System.Data.Services.Client.AtomMaterializer.Materialize(AtomEntry entry, Type expectedEntryType, Boolean includeLinks) at System.Data.Services.Client.AtomMaterializer.DirectMaterializePlan(AtomMaterializer materializer, AtomEntry entry, Type expectedEntryType) at System.Data.Services.Client.AtomMaterializerInvoker.DirectMaterializePlan(Object materializer, Object entry, Type expectedEntryType) at System.Data.Services.Client.ProjectionPlan.Run(AtomMaterializer materializer, AtomEntry entry, Type expectedType) at System.Data.Services.Client.AtomMaterializer.Read() at System.Data.Services.Client.MaterializeAtom.MoveNextInternal() at System.Data.Services.Client.MaterializeAtom.MoveNext() at System.Linq.Enumerable.d_b11.MoveNext() at System.Data.Services.Client.DataServiceCollection1.InternalLoadCollection(IEnumerable1 items) at System.Data.Services.Client.DataServiceCollection1.StartTracking(DataServiceContext context, IEnumerable1 items, String entitySet, Func2 entityChanged, Func2 collectionChanged) at System.Data.Services.Client.DataServiceCollection1..ctor(DataServiceContext context, IEnumerable1 items, TrackingMode trackingMode, String entitySetName, Func2 entityChangedCallback, Func2 collectionChangedCallback) at System.Data.Services.Client.DataServiceCollection1..ctor(IEnumerable1 items) at Phinli.Dashboard.Silverlight.Helpers.DataHelper.<>c__DisplayClass44.<>c__DisplayClass46.<LoadAllPagesExpandAll>b__43() InnerException: System.InvalidOperationException Message=An item could not be added to the collection. When items in a DataServiceCollection are tracked by the DataServiceContext, new items cannot be added before items have been loaded into the collection. StackTrace: at System.Data.Services.Client.DataServiceCollection1.InsertItem(Int32 index, T item) at System.Collections.ObjectModel.Collection`1.Add(T item) InnerException:

Thanks for any help!