c# – nHibernate,将两个属性映射到同一个类

public class dbMail : Entity
{
    public virtual int ThreadID { get; set; }
    public virtual dbUser From { get; set; }
    public virtual dbUser To { get; set; }
    public virtual DateTime MailDate { get; set; }
    public virtual string MailText { get; set; }
    public virtual bool IsRead { get; set; }
}

和映射：
????

<id name="ID">
  <generator class="identity" />
</id>
<property name="ThreadID" />

<many-to-one name="From" class="dbUser" column="From"/>
<many-to-one name="To" class="dbUser" column="To"/>
<property name="MailDate" />
<property name="MailText" type="StringClob">
  <column name="MailText" sql-type="text" />
</property>
<property name="IsRead" />

但是,尝试更新数据库时,会发生此错误：

Duplicate property mapping of dbUser found in Domain.Model.dbMail