I am getting the following error message when I try to update/add a new record in table A.

javax.servlet.ServletException: object references an unsaved transient instance - save the transient instance before flushing: com.company.struts.project.ParentClass

I have two tables TableA & TableB. The relationship is TableB 1->many TableA. The configuration files are set accordingly.

<!-- Table B config -->
<set name="TableB" inverse="false">
<key column="SId" />
<one-to-many entity-name="TableA" />
</set>

<!-- Table A config -->
<many-to-one name="TableB"
column="SId" not-null="false"
entity-name="TableA" />

So, whenever I try to update the SId column in Table A (nullable) to set to Null (this value in not in Table B, as it is primary key), the above error is being thrown.

I am sorry if I was incoherent in my explanation. Any help is greatly appreciated.

Set the inverse attribute to true: