NHibernate中使用generator为assigned的问题

Hibernate version:
1.0.2.0
Mapping documents:
Parent.hbm.xml

<? xml version="1.0" encoding="utf-8" ?>

< hibernate-mapping xmlns ="urn:nhibernate-mapping-2.0" >

< class name ="HYLQ.Core.Domain.Parent, HYLQ.Core" table ="Parent" >

< id name ="Id" column ="Id" unsaved-value ="0" >

< generator class ="assigned" />

</ id >

< property name ="Title" type ="String" length ="200" />

< bag name ="Childs" lazy ="true" table ="Child" inverse ="true" cascade ="all"

access ="NHibernate.Generics.GenericAccessor, NHibernate.Generics" >

< key column ="pid" />

< one-to-many class ="HYLQ.Core.Domain.Child, HYLQ.Core" />

</ bag >

</ class >

</ hibernate-mapping >

Child.hbm.xml

<? xml version="1.0" encoding="utf-8" ?>

< hibernate-mapping xmlns ="urn:nhibernate-mapping-2.0" >

< class name ="HYLQ.Core.Domain.Child, HYLQ.Core" table ="Child" >

< id name ="Id" column ="Id" unsaved-value ="0" >

< generator class ="assigned" />

</ id >

< property name ="Memo" type ="String" length ="200" />

< many-to-one name ="Parent" column ="pid" class ="HYLQ.Core.Domain.Parent, HYLQ.Core"

access ="NHibernate.Generics.GenericAccessor, NHibernate.Generics" />

</ class >

</ hibernate-mapping >

测试代码：

using (ISession session = TestCategory.Factory.OpenSession())

{

int id = 1;

Parent parent = new Parent();

parent.Id = id;

parent.Title = "tetetet";

Child child = new Child();

child.Id = 1;

child.Memo = "222";

child.parent = parent;

parent.Childs.Add(child);

ITransaction trans = session.BeginTransaction();

try

{

session.Save(parent);

trans.Commit();

}

catch

{

trans.Rollback();

throw;

}

当我设置了
chilid.Id =1的时候，则出现了
Test method TestProject1.TestCategory.AddParentChild threw exception: NHibernate.HibernateException: SQL insert, update or delete failed (expected affected row count: 1, actual affected row count: 0). Possible causes: the row was modified or deleted by another user, or a trigger is reporting misleading row count..
跟踪执行的SQL语句后，发现并不是Insert Child，而是Update Child。
当我将chilid.Id =1注释后，就正常，不过chilid.Id他用 unsaved-value="0"代替。
执行的SQL语句都是正常的。

而我在网上看到一些One2Many的例子中其中表的主键都是自增长的后非assigned的。
所以这个问题很是困惑，最后，自己写了一个自定义的Generator来生产ID,
后来就没有出现上述的情况了。

你们碰到过这种情况吗？