如何获得完整的对象与代码优先实体框架4.1

我试图返回JSON完全深的对象(与所有的外键关系填写)，但我得到所有引用的对象为空。

下面是获取对象的调用:

    public ActionResult GetAll()
    {
        return Json(ppEFContext.Orders, JsonRequestBehavior.AllowGet);
    }

这里是Order对象本身:

public class Order
{
    public int Id { get; set; }
    public Patient Patient { get; set; }
    public CertificationPeriod CertificationPeriod { get; set; }
    public Agency Agency { get; set; }
    public Diagnosis PrimaryDiagnosis { get; set; }
    public OrderApprovalStatus ApprovalStatus { get; set; }
    public User Approver { get; set; }
    public User Submitter { get; set; }
    public DateTime ApprovalDate { get; set; }
    public DateTime SubmittedDate { get; set; }
    public Boolean IsDeprecated { get; set; }
}

我还没有找到一个很好的资源使用EF 4.1注释。如果你能建议一个好的，有答案的，你可以给我链接，这对我来说就足够了!

问候,圭多

我添加了虚拟关键字按萨克斯曼和我现在处理循环引用误差问题。

public class Order
{
    public int Id { get; set; }
    public virtual Patient Patient { get; set; }
    public virtual CertificationPeriod CertificationPeriod { get; set; }
    public virtual Agency Agency { get; set; }
    public virtual Diagnosis PrimaryDiagnosis { get; set; }
    public virtual OrderApprovalStatus ApprovalStatus { get; set; }
    public virtual User Approver { get; set; }
    public virtual User Submitter { get; set; }
    public DateTime ApprovalDate { get; set; }
    public DateTime SubmittedDate { get; set; }
    public Boolean IsDeprecated { get; set; }
}