There is a NHibernate problem torturing me right now.I have two class,one is SysPerson,the other is SysDepartment.The relationship between the two classes is many to one. I got the SysPerson from ISession,and modify it in detached state.Any modification but the property referencing the SysDepartment will be safely updated to database.Every operation to change the property named SysDepartment will get the Exception Message:identifier of an instance of Authorization.SysDepartment was altered from 001 to 002. I just modify the reference by switch the reference to the other SysDepartment instance after the session closed.I thought the NHibernate have the ability to find the way to just change the FK value in SysPerson,but indeed NHibernate is tring to modify the PK value in SysDepartment.I think maybe there is some way to change the Mapping file to fix this problem. Please help me out of this dilemma.Thank you!

Sounds like you try to change the id of the department

sysPerson.SysDepartment.Id = "002";

That's not possible, you have to set the complete object:

sysPerson.SysDepartment = department002;

Thanks to wolli. I did the same way you suggested, but the result let me down. I thought the problem may be the my SysPerson instance and SysDepartment instance come from different ISession. So when I set the sysPerson.SysDepartment = department002,NHibernate try to change the original SysDepartment by update its ID by department002. I go into the break point, I also found that when I have done sysPerson.SysDepartment = department002,I couldn't get the all SysDepartment from ISession,because of the same problem:identifier of an instance of Authorization.SysDepartment was altered from 001 to 002. I need the operation which load all SysDepartments information from New ISession for user to change the SysPerson's property SysDepartment that come from first ISession. Any one have suggestion for help me out.

Can you post your code ? And the relevant part of the mapping files ?

Thank you,Really! I fix my problem. Although I hadn't change the ID of SysDepartment, but in my code there is a databinding:[comboBox.DataBindings.Add("Value", SysDepartments, "ID")] which I want to use to present current SysDepartment.When I removed the databinding, everything is ok.What a stupid mistake I made. I think it's very careful for us to using the databinding with NHibernate detached object.