I have Student object which holds reference to ID of Address object.

I read the Student object and update the referred parent.
When I use unique non primary key from the referred/parent object I face no problems.

When my association refers to primary key and not unique key of parent then I face problems
Problem faced when Relationship mapped as

<many-to-one name="StudentAddress" name="com.san.Address" fetch="join" unique="true" update="true" insert="true" optimistic-lock="true" not-found="exception" embed-xml="true">
<column name="AddressID" not-null="true"/>
</many-to-one>

NO PROBLEM when:

<many-to-one name="StudentAddress" property-ref="UK_Address" name="com.san.Address" fetch="join" unique="true" update="true" insert="true" optimistic-lock="true" not-found="exception" embed-xml="true">
<column name="pinCode" not-null="true"/>
<column name="country" not-null="true"/>
</many-to-one>



my parent class is:
<class name="com.san.Address" table="Address" dynamic-insert="true" mutable="true" polymorphism="implicit" dynamic-update="false" select-before-update="false" optimistic-lock="version">
<id name="ID" type="java.lang.Long" column="ID">
<generator class="native"/>
</id>
<properties name="UK_Address" unique="true" update="true" insert="true" optimistic-lock="true">
<property name="PinCode" type="java.lang.Long" column="PinCode" unique="false" optimistic-lock="true" lazy="false" generated="never"/>
<property name="Country" type="java.lang.String" column="Country" unique="false" optimistic-lock="true" lazy="false" generated="never"/>
</properties>

</class>



Caused by:
org.hibernate.HibernateException: identifier of an instance of Address was a
ltered from 3 to 2
at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(Defau
ltFlushEntityEventListener.java:58)
at org.hibernate.event.def.DefaultFlushEntityEventListener.getValues(Def
aultFlushEntityEventListener.java:164)
at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity
(DefaultFlushEntityEventListener.java:120)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(A
bstractFlushingEventListener.java:196)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverything
ToExecutions(AbstractFlushingEventListener.java:76)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlus
hEventListener.java:26)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)

This issue was resolved , by creating a new object of Address with the given id and replacing the object associated with object Student.