無法從WCF數據服務返回自定義類

Question

我想從我的WCF數據服務返回自定義類。我的自定義類是：

[DataServiceKey("ID")] 
public class Applist { 
    public int ID { get; set; } 
    public string Name { get; set; } 
} 

我的數據服務看起來像：

public static void InitializeService(IDataServiceConfiguration config) 
{ 
    config.RegisterKnownType(typeof(Applist)); 
    config.SetEntitySetAccessRule("*", EntitySetRights.All); 
    config.SetServiceOperationAccessRule("GetApplications", ServiceOperationRights.AllRead); 
} 

[WebGet] 
public IQueryable<Applist> GetApplications() { 
    var result = (from p in this.CurrentDataSource.Applications 
      orderby p.ApplicationName 
      group p by p.ApplicationName into g 
      select new Applist { ID = g.Min(p => p.id), Name = g.Key }); 

    return result.AsQueryable(); 
} 

然而，當我運行的服務，它給了我一個錯誤：

Request Error Request Error The server encountered an error processing the request. 
The exception message is 'Unable to load metadata for return type 
'System.Linq.IQueryable`1[ApplicationService.Applist]' of method 
'System.Linq.IQueryable`1[ApplicationService.Applist] GetApplications()' 

同樣的查詢完美運行在LINQPad中很好。

Answer 1

請參閱以下博客。它解釋了這種情況，並詳細一個可能的解決方案： http://samuelmueller.com/2009/11/working-with-projections-and-dtos-in-wcf-data-services/