ObjectQuery error when using STE and WCF

Question

I received this error when i implement STE in EF4 and WCF

"Object mapping could not be found for Type with identity 'NorthwindModel.Customer'."

if I'm not using STE (in single project), this code is working.

Walkthrough: Serialize Self-Tracking Entities

Here is my code

WCF:

Public Class Service1
Implements IService1

  Public Function GetData(ByVal query As String) As List(Of DbDataRecord) Implements IService1.GetData
  Try
     Using ctx = New NorthwindEntities()
        Return New ObjectQuery(Of DbDataRecord)(query, ctx).ToList 'Here is the error.
     End Using
  Catch ex As Exception
     Dim theFault As New ServFault()
     theFault.Reason = ex.Message.ToString()
     Throw New FaultException(Of ServFault)(theFault, ex.Message.ToString)
  End Try
End Function

Public Function GetOrderByCustomer(customerId As String) As System.Collections.Generic.List(Of Entities.Order) Implements IService1.GetOrderByCustomer
  Try
     Using ctx = New NorthwindEntities()
        Return (From ord In ctx.Orders Where ord.CustomerID = customerId).ToList
     End Using
  Catch ex As Exception
     Dim theFault As New ServFault()
     theFault.Reason = ex.Message.ToString()
     Throw New FaultException(Of ServFault)(theFault, ex.Message.ToString)
  End Try

End Function
End Class

WCF Config

<?xml version="1.0"?>
<configuration>

  <system.web>
    <compilation debug="true" strict="false" explicit="true" targetFramework="4.0" />
  </system.web>
  <system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
  </system.webServer>
   <connectionStrings>
      <add name="NorthwindEntities" connectionString="metadata=res://*/NWDModel.csdl|res://*/NWDModel.ssdl|res://*/NWDModel.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=(local);initial catalog=Northwind;persist security info=True;user id=sa;password=145837;multipleactiveresultsets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
   </connectionStrings>
</configuration>

WCF Client:

Module Module1

   Sub Main()
      Dim srv As New Service1Client
      Dim query As String
      Dim lst As List(Of DbDataRecord)

      Console.WriteLine("Start...")

      Dim orders As List(Of Entities.Order)
      orders = srv.GetOrderByCustomer("ALFKI") 'This code is working
      Console.WriteLine("Success!!! Order Count: {0}", orders.Count)

      query = "SELECT p FROM Customers AS p"
      lst = srv.GetData(query)

      Console.WriteLine("Total Customer: {0}", lst.Count)

      srv.Close()
      Console.ReadLine()
   End Sub

End Module

Hope somebody can guide me. Full source for above sample also available if you need it

Answer 1

This will not work over WCF. You must always send real entity type back, not the DbDataRecord which is abstract class. WCF must know what is the real type used. The real type in EF is probably MaterializedDbRecord which is internal and non-serializable.

When exposing methods over WCF you must use simple types or data contracts / serializalbe types as parameters and results. STEs are data contracts so use them directly - that obviously breaks your requirement to send untyped queries from the client but it is not scenario for WCF.

If you are looking for technology which will allow you creating queries on the client check WCF Data Services (but they don't support STEs).