Failed to invoke the service when the method returns List

Question

I am new to wcf and I have a simple question.

I use EF with WCF service. WCF service called from WinForms app. I want get simple List from WCF. When i invoke AllVisitors() from wcf test console i get next error:

Failed to invoke the service. Possible causes: The service is offline or inaccessible; the client-side configuration does not match the proxy; the existing proxy is invalid. Refer to the stack trace for more detail. You can try to recover by starting a new proxy, restoring to default configuration, or refreshing the service.

In trace log i see next exaption:

There was an error while trying to serialize parameter http://tempuri.org/:AllVisitorsResult. The InnerException message was 'Type 'System.Data.Entity.DynamicProxies.Visitor_4E7A6F28B7631289C58E0883F6BDF681C78B7180EA3E530CDFE420CAA3C15645' with data contract name Visitor_4E7A6F28B7631289C58E0883F6BDF681C78B7180EA3E530CDFE420CAA3C15645:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types – for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

Here is my code:

[ServiceContract]
public interface IServiceVisit
{
    [OperationContract]
    [WebInvoke(BodyStyle = WebMessageBodyStyle.WrappedResponse)]
    List<Visitor> AllVisitors();
}

[DataContract]
[KnownType(typeof(Visitor))]
[KnownType(typeof(Visit))]
[KnownType(typeof(ICollection<Visit>))]
public class ServiceVisit : IServiceVisit
{
    public List<Visitor> AllVisitors()
    {
        using (TurnstileDbEntities te = new TurnstileDbEntities())
        {
            return te.Visitors.ToList<Visitor>();
        }
    }
}

The method fails when I try return a List<Visitor>. But the method works perfectly fine when I return a primitive type. Such as int, decimal, string...etc.

Here Visitor and Visit auto generated model:

public partial class Visitor
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Visitor()
    {
        this.Visits = new HashSet<Visit>();
    }

    public int Id { get; set; }
    public int PermitId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string MiddleName { get; set; }
    public bool IsValid { get; set; }
    public System.DateTime RegistrationDate { get; set; }
    public byte[] Picture { get; set; }
             [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Visit> Visits { get; set; }
}

public partial class Visit
{
    public int Id { get; set; }
    public int VisitType { get; set; }
    public System.DateTime VisitDate { get; set; }
    public Nullable<int> Visitor_Id { get; set; }

    public virtual Visitor Visitor { get; set; }
}

I know that List<> is populated with data. And I know that size of data can be big because byte[] Picture contains binary data (images). Also Visitor related to Visit as one to many. As I understood problem is in serialization and in generated dynamic proxies with names like: Visitor_4E7A6F28B7631289C58E0883F6BDF681C78B7180EA3E530CDFE420CAA3C15645. But maybe I'm wrong. So, how can I fix this issue and what am I doing wrong? I found that this issue disscused regulary. But can't find solution for me.

Answer 1

So, solution for this isssue is to set ProxyCreationEnabled = false

    public List<Visitor> AllVisitors()
    {

        using (TurnstileDbEntities te = new TurnstileDbEntities())
        {
            te.Configuration.ProxyCreationEnabled = false;
            return te.Visitors.ToList<Visitor>();
        }
    }