i have an object A depending to an object B. A is mapped with a many-to-one-relationship in mapping file of B. the ID of B is an not-null-field in table of A. my problem is that A will be saved earlier than B and because of B is not saved yet I get a NOtNullViolationException from database.

Mapping B:
<hibernate-mapping>
<class name="com.carano.cbf.kalkulation.po.NachlassPO" table ="NACHLASS">
<jcs-cache usage="read-write"/>
<id name="ID">
<column name="NACHLASS_ID" sql-type="int"/>
<generator class="fleet.kalkulation.persistence.AppIdGenerator"/>
</id>
....
<!-- DepBO -->
<many-to-one
name="fahrzeuggeltungsbereich"
column="NACHLASS_ID" class="com.carano.automotive.fahrzeug.po.FahrzeuggeltungsbereichPO"
cascade="all"
outer-join="auto"
update="false"
insert="false"
/>
....
</class>
</hibernate-mapping>

1. save(B) then save (A)
2. add a one-to-many to B, cascaded and save B (as per the parent child relationship in refrence guide)

i'm sure that the second case (parent-child-relation) will solve my problem. but when I tried this I got a classcastexception, because now I mapped this relation as a Set but I have just one child and don't need a set. so what can I do?

one-to-one ?