如何在EF 4.1代码优先中建立外键关系

所以我整个上午都在纠结这个问题。我读了一些文章，我的工作大致基于这一篇:

http://weblogs.asp.net/manavi/archive/2011/01/23/associations-in-ef-code-first-ctp5-part-3-one-to-one-foreign-key-associations.aspx

这是我当前的错误:

在序列化类型为"system . data . entity . dynamicagents . order_c00ce366506bd8c6592a3cf21b9d1c5921d31c03d7322a8f6e8ead72e113ea95"的对象时检测到循环引用。

下面是类:

public class Order
{
    [Key]
    public int OrderId { get; set; }
    public int PatientId { get; set; }
    public virtual Patient Patient { get; set; }
    public int CertificationPeriodId { get; set; }
    public virtual CertificationPeriod CertificationPeriod { get; set; }
    public int AgencyId { get; set; }
    public virtual Agency Agency { get; set; }
    public int PrimaryDiagnosisId { get; set; }
    public virtual Diagnosis PrimaryDiagnosis { get; set; }
    public int ApprovalStatusId { get; set; }
    public virtual OrderApprovalStatus ApprovalStatus { get; set; }
    public int UserId { get; set; }
    public virtual User Approver { get; set; }
    public int SubmitterId { get; set; }
    public virtual User Submitter { get; set; }
    public DateTime ApprovalDate { get; set; }
    public DateTime SubmittedDate { get; set; }
    public Boolean IsDeprecated { get; set; }
}

我假设我已经做了一些"流畅的API。"不幸的是，我对fluent API并不熟练，所以我想验证一下，这实际上就是所缺少的。

谢谢,

圭多