Entity Framework 4 allows us to create complex types. Typically, such types are used to get the result of a stored procedure. However, when we try to send such a complex type using a WCF RIA Domain Service, the following error is encountered.



What to do? Adding attributes to EF designer generated classes is a bad idea; Also, we cannot use partial classes to add attributes to an already defined property. However, luckily, WCF RIA Services uses metadata classes in conjunction with the entity model classes and hence we can always create a meta data class for our complex type and decorate one of the fields with a [Key] attribute. E.g., If our stored procedure is returning StoredProcedure_Result, then we may just need to add the following in our DomainService.metadata.cs file: