NHibernate级联未设置外键

正如标题所述，父级和子级都被插入到数据库中，但没有被链接。

映射请求

  <class name="Request" table="Requests">
<id name="RequestId">
  <generator class="native" />
</id>
<many-to-one name="BulkReport" class="BulkReport" column="BulkId" cascade="none" lazy="proxy" />
<property name="RunNumber" />
<property name="MobileNumber" />
<property name="Message" />
<property name="RequestedOn" />
<property name="Closed" />
<many-to-one name="Communication" class="Communication" column="CommId" cascade="save-update" lazy="proxy" />
<many-to-one name="Outcome" class="Outcome" column="OutcomeId" cascade="none" lazy="proxy" />
<many-to-one name="Discount" class="Discount" column="Discount" not-found="ignore" cascade="save-update" lazy="proxy" />
</class>

映射折扣

  <class name="Discount" table="Discounts" discriminator-value="BASE">
<id name="DiscountId">
  <generator class="native" />
</id>
<discriminator column="DiscountType" not-null="true" />
<property name="MobileNumber" />
<property name="CustomerName" />
<property name="AddedOn" />
<property name="Status" />
<property name="Pending" />
<many-to-one name="Product" class="DiscountProduct" column="DiscountProduct" cascade="none" lazy="proxy" />
<many-to-one name="AddedBy" class="User" cascade="none" lazy="proxy" />
<subclass name="StaffDiscount" discriminator-value="STAFF">
  <many-to-one name="Employee" class="Employee" column="EmployeeNumber" cascade="none" lazy="proxy" not-null="false" />
</subclass>
</class>

来自测试的SQL

NHibernate: INSERT INTO Discounts (MobileNumber, CustomerName, AddedOn, Status,          Pending, DiscountProduct, AddedBy, DiscountType) VALUES (?, ?, ?, ?, ?, ?, ?, 'BASE');@p0 = 700000000, @p1 = 'Test', @p2 = 25/06/2013 14:38:43, @p3 = True, @p4 = False, @p5 = 1, @p6 = 'Test'
NHibernate: select @@identity
NHibernate: INSERT INTO Requests (BulkId, RunNumber, MobileNumber, Message, RequestedOn, Closed, CommId, OutcomeId, Discount) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);@p0 = 1, @p1 = 100, @p2 = 700000000, @p3 = 'Test Request', @p4 = 25/06/2013 14:38:43, @p5 = True, @p6 = NULL, @p7 = 1, @p8 = 0
NHibernate: select @@identity

知道为什么会发生这种事吗？对此有完整的了解吗？

编辑：请求的信息

折扣类别

    public class Discount
{
    public virtual int DiscountId { get; set; }
    public virtual double MobileNumber { get; set; }
    public virtual string CustomerName { get; set; }
    public virtual DateTime AddedOn { get; set; }
    public virtual bool Status { get; set; }
    public virtual bool Pending { get; set; }
    public virtual DiscountProduct Product { get; set; }
    public virtual User AddedBy { get; set; }
    public override string ToString()
    {
        return "0" + MobileNumber + ", " + CustomerName.Trim();
    }
}

请求类

    public class Request
{
    public virtual int RequestId { get; set; }
    public virtual BulkReport BulkReport { get; set; }
    public virtual int RunNumber { get; set; }
    public virtual double MobileNumber { get; set; }
    public virtual string Message { get; set; }
    public virtual DateTime RequestedOn { get; set; }
    public virtual Outcome Outcome { get; set; }
    public virtual bool Closed { get; set; }
    public virtual Communication Communication { get; set; }
    public virtual Discount Discount { get; set; }
}

测试I运行

        [Test]
    public void Can_add_new_request_with_discount()
    {
        ISession session = _sessionFactory.OpenSession();
        BulkReport report = session.Get<BulkReport>(1);
        Outcome outcome = session.Get<Outcome>(1);
        User user = session.Get<User>("Test");
        DiscountProduct discountProduct = session.Get<DiscountProduct>(1);

        Request request = new Request()
        {
            Message = "Test Request",
            BulkReport = report,
            Closed = true,
            MobileNumber = 07000000000,
            RequestedOn = DateTime.Now,
            RunNumber = 100,
            Outcome = outcome
        };
        Discount discount = new Discount
            {
                AddedBy = user,
                AddedOn = DateTime.Now,
                CustomerName = "Test",
                MobileNumber = 07000000000,
                Pending = false,
                Status = true,
                Product = discountProduct
            };
        request.Discount = discount;
        session.Save(request);
        var fromDbRequest = session.Get<Request>(request.RequestId);
        var fromDbDiscount = session.Get<Discount>(discount.DiscountId);
        Assert.IsNotNull(fromDbRequest);
        Assert.IsNotNull(fromDbDiscount);
        Assert.AreEqual(request.MobileNumber, fromDbRequest.MobileNumber);
        Assert.AreEqual(discount.MobileNumber, fromDbDiscount.MobileNumber);
        session.Close();
    }