Nhibernate 双向映射

无论如何，如何创建两个类，它们将被双向引用，并且只使用一个FK？这使我对一对一和一对多的情况感兴趣

f、 e:

Class First: Entity
{
Second second;
}

Class Second: Entity
{
First first;
}

String TwoWayReference()
{
First Fir = new First();
Second Sec = new Second();

Fir.second = Sec; // I need it is equivalent to: Sec.first = Fir;

if (Sec.first == Fir)
    return "Is any way how to do this code works and code return this string?";
else
    return "Or it is impossible?"
}

最简单的是

class First : Entity
{
    private Second second;
    public virtual Second Second
    {
        get { return this.second; }
        set {
            if (value != null)
            {
                value.First = this;
                this.second = value;
            }
        }
    }
}

class Second : Entity
{
    private First first;
    public virtual First First
    {
        get { return this.first; }
        set {
            if (value != null && value.Second != this)
            {
                value.Second = this;
                this.first = value;
            }
        }
    }
}

---

问题是，有时值为null，例如，如果我创建新实例，则为null引用异常：对象引用未设置为对象的实例。如果我在值为null时对其进行测试，则会出现stackowerflow问题—它会为第一个实例创建第二个实例，为第二个实例创建第一个实例