Mapping documents:

<hibernate-mapping>
<class name="model.Unit" table="UNIT">
<id name="id" type="string" unsaved-value="null">
<column name="UNITID"/>
<generator class="uuid.hex"/>
</id>
<property name="name" column="NAME" not-null="true"/>
<property name="description" column="DESCRIPTION"/>
<many-to-one name="parentUnit" column="PARENT_UNITID" class="model.Unit"/>
<set name="units" table="UNIT" cascade="all" lazy="true" inverse="true">
<key column="PARENT_UNITID"/>
<one-to-many class="model.Unit"/>
</set>
</class>
</hibernate-mapping>


Unit.java:

public class Unit {
private String id = null;
private String name = null;
private String description = null;
private Unit parentUnit = null;
private Set units = new HashSet();
// getter and setter methods
}


When I want to update an unit, I got the exceptions below, the save method works well.

Full stack trace of any exception that occurs:

net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 2c9081b90238110701023811a13a0003, of class: model.Unit
at net.sf.hibernate.impl.SessionImpl.checkUniqueness(SessionImpl.java:1686)
at net.sf.hibernate.impl.SessionImpl.doUpdateMutable(SessionImpl.java:1452)
at net.sf.hibernate.impl.SessionImpl.doUpdate(SessionImpl.java:1479)
at net.sf.hibernate.impl.SessionImpl.update(SessionImpl.java:1364)
......


Thank you in advance!