我有一个实体定义如下（代码由VS2010 POCO生成器生成）：

public partial class TransactionList
    {
        public int tlRecordId { get; set; }
        public Nullable<int> tlTracer { get; set; }
        public Nullable<int> tlRecordType { get; set; }
        public Nullable<int> tlPayType { get; set; }
        public Nullable<int> pdmNumber { get; set; }
        public string pdmName { get; set; }
        public string zoneName { get; set; }
        public string groupName { get; set; }
        public Nullable<int> serviceCarNumber { get; set; }
        public Nullable<int> moneyCarNumber { get; set; }
        public Nullable<System.DateTime> tlPayDateTime { get; set; }
        public Nullable<System.DateTime> tlExpDateTime { get; set; }
        public Nullable<int> senderPdmNumber { get; set; }
        public Nullable<int> tlAmount { get; set; }
        public Nullable<int> tlTicketNo { get; set; }
    }

并且对于这个类存在第二个部分类（手动编写），该部分类包含Key属性。

[DataServiceKey("tlRecordId")]
public partial class TransactionList
{ }

因此，在这个类中没有定义复杂的类型/基元集合。如果我使用WCF数据服务公开此类，我会得到以下异常：

The server encountered an error processing the request. The exception message is The property TransactionList on type DomainObjects.EntityFrameworkModel.Gac is not a valid property. Properties whose types are collection of primitives or complex types are not supported. . See server logs for more details. The exception stack trace is:

at System.Data.Services.Providers.ReflectionServiceProvider.BuildTypeProperties(ResourceType parentResourceType, IDictionary2 knownTypes, IDictionary2 childTypes, Queue1 unvisitedTypes, IEnumerable1 entitySets) at System.Data.Services.Providers.ReflectionServiceProvider.PopulateMetadataForTypes(IDictionary2 knownTypes, IDictionary2 childTypes, Queue1 unvisitedTypes, IEnumerable1 entitySets) at System.Data.Services.Providers.ReflectionServiceProvider.PopulateMetadata(IDictionary2 knownTypes, IDictionary2 childTypes, IDictionary2 entitySets) at System.Data.Services.Providers.BaseServiceProvider.PopulateMetadata() at System.Data.Services.DataService1.CreateProvider() at System.Data.Services.DataService1.EnsureProviderAndConfigForRequest() at System.Data.Services.DataService1.HandleRequest() at System.Data.Services.DataService`1.ProcessRequestForMessage(Stream messageBody) at SyncInvokeProcessRequestForMessage(Object , Object[] , Object[] ) at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage41(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage11(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)

类Gac包含如下定义的属性TransactionList：

public IQueryable<TransactionList> TransactionList
{
  get { return _myContext.TransactionList.AsNoTracking(); }
}

Why do I get this exception? I do not see any helpful information in the WCF server log. One useful information for you can be that this entity is representing a database view. I already expose a similar entity which contains the same types of properties int, DateTime, string) and it is working.

** UPDATE ** Data service definiton added (I left out the IDisposable methods):

public class DummyService : DataService<CustomContext>
{
  protected override CustomContext CreateDataSource()
  {
     //I need a single endpoint exposing data from more databases. Here I pass
     //the data needed for the creation of connection strings
     var dataSource = new CustomContext(new int []{1,2,3});
     return dataSource;
   }
}

///This class represents my single endpoint exposing data from various databases.
///Every database has the same DB schema.
public class CustomContext: IDisposable
{
  private static IList<Gac> _gacList;

  //Here I construct the list of accessible data sources - databases. This list
  // can vary
  public CustomContext(IEnumerable<AreaCodes> areaCodes)
  {
    //This is the list of various databases exposed via OData
    _gacList = new List<Gac>();

    foreach (AreaCodes ac in areaCodes)
    {
      //When calling the constructor of Gac, the DbContext gets created.
      _gacList.Add(new Gac(ac.Id));
    }
  }

  //the entity which will be exposed
  public IQueryable<Gac> Gac
  {
      get { return _gacList != null ? _gacList.AsQueryable() : null; }
  }
}

///This class represents a single data source - a database. 
//All databases are exposed over single endpoint
[DataServiceKey("GacId")]
public class Gac: IDisposable
{
    private MyContext _myContext;
    private int _gacId;

  public Gac(int areaCode)
  {
    //Here I finally create my context
    _myContext= new MyContext("...Connection String Generated based on areaCode");
    _myContext.Configuration.ProxyCreationEnabled = false;
    _myContext.Configuration.LazyLoadingEnabled = false;

    _gacId = areaCode;
  }  

  //This property uniquely identifies a GAC object. It is an entity key.
  public int GacId
  {
    get { return _gacId; }
  }

  //Expose an entity from the EF layer
  public IQueryable<TransactionList> TransactionList
  {
    get { return _myContext.TransactionList.AsNoTracking(); }
  }

  //...Other about 25 IQueryable properties
}

//generated Entity Framework Conceptual Layer
public partial class MyContext: DbContext
{
  //This entity represents my database view which I want to access to
  public DbSet<TransactionList> TransactionList { get; set; }
  //...Other about 25 generic DbSet properties
}