WCF data services (OData), query with inheritance limitation?

Question

Project: WCF Data service using internally EF4 CTP5 Code-First approach.

I configured entities with inheritance (TPH). See previous question on this topic:

Previous question about multiple entities- same table

The mapping works well, and unit test over EF4 confirms that queries runs smoothly.

My entities looks like this:

• ContactBase (abstract)
• Customer (inherits from ContactBase), this entity has also several Navigation properties toward other entities
• Resource (inherits from ContactBase)

I have configured a discriminator, so both Customer and Resource map to the same table. Again, everythings works fine on the Ef4 point of view (unit tests all greens!)

However, when exposing this DBContext over WCF Data services, I get: - CustomerBases sets exposed (Customers and Resources sets seems hidden, is it by design?) - When I query over Odata on Customers, I get this error:

Navigation Properties are not supported on derived entity types. Entity Set 'ContactBases' has a instance of type 'CodeFirstNamespace.Customer', which is an derived entity type and has navigation properties. Please remove all the navigation properties from type 'CodeFirstNamespace.Customer'. 

Stacktrace:

at System.Data.Services.Serializers.SyndicationSerializer.WriteObjectProperties(IExpandedResult expanded, Object customObject, ResourceType resourceType, Uri absoluteUri, String relativeUri, SyndicationItem item, DictionaryContent content, EpmSourcePathSegment currentSourceRoot)
at System.Data.Services.Serializers.SyndicationSerializer.WriteEntryElement(IExpandedResult expanded, Object element, ResourceType expectedType, Uri absoluteUri, String relativeUri, SyndicationItem target)
at System.Data.Services.Serializers.SyndicationSerializer.<DeferredFeedItems>d__b.MoveNext()
at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteItems(XmlWriter writer, IEnumerable`1 items, Uri feedBaseUri)
at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeedTo(XmlWriter writer, SyndicationFeed feed, Boolean isSourceFeed)
at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeed(XmlWriter writer)
at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteTo(XmlWriter writer)
at System.Data.Services.Serializers.SyndicationSerializer.WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, Boolean hasMoved)
at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved)
at System.Data.Services.ResponseBodyWriter.Write(Stream stream)

Seems like a limitation of WCF Data services... is it? Not much documentation can be found on the web about WCF Data services (OData) and inheritance specifications.

How can I overpass this exception? I need these navigation properties on derived entities, and inheritance seems the only way to provide mapping of 2 entites on the same table with Ef4 CTP5...

Any thoughts?

Answer 1

Currently, WCF data services does not support navigation properties on derived types. This is a known limitation and we are currently working on enabling this for our next release.

Currently, the work around is that you put all the navigation properties to the type refered by the set. In your example, can you make the entity set type be customer, instead of ContactBase?

Hope this helps. Thanks Pratik