为什么我的对象不需要ServiceKnownType?

[ServiceContract(CallbackContract = typeof(IMyServiceCallback))]
public interface IMyService
{
    [OperationContract]
    List<MyObject> LoadMyObjects();
}

[DataContract]
public class MyObject
{
    [DataMember]
    private int batchID;
    [DataMember]
    private int fileID;
    [DataMember]
    private string fileName;
    [DataMember]
    private DateTime importStartTime;
// ...
}