Question

Could somebody explain me how to map a one-to-zero association with hibernate (using mapping xml files NOT annotations)?

These are the rules:

• A Menu can have 0 or 1 Area associated.
• An Area belongs to a Menu. (Or, if it is easier for you to modelize it: An Area can have 0 or 1 Menu associated).

Here are the desired TABLES (I want to use foreign keys):

TABLE MENU:
ID
NAME
FKID_AREA

TABLE AREA:
ID
NAME
FKID_MENU

Thanks!

Answer 1

You should remove the FKID_AREA from the MENU table, because it’s not needed (and is even a problem, since it’s redendant with AREA.FKID_MENU).

For the rest, this is described in the Hibernate documentation on bidirectional one-to-one association mappings:

<class name="Area">
    <id name="id" column="ID">
        <generator class="native"/>
    </id>
    <many-to-one name="menu" 
        column="FKID_MENU" 
        unique="true"
        not-null="false"/>
</class>

<class name="Menu">
    <id name="id" column="ID">
        <generator class="native"/>
    </id>
   <one-to-one name="area" 
        property-ref="menu"/>
</class>