Configuring a Many-to-One Relationship

In a many-to-one relationship, multiple instances of an entity bean may be related to a single instance of another entity bean. This multiplicity is the opposite of one-to-many.

You specify a container-managed many-to-one relationship in the ejb-jar.xml deployment descriptor (see "Using Deployment XML").

For more information, see "Configuring a Container-Managed Relationship Field for an EJB 2.1 Entity Bean With Container-Managed Persistence".

Using Deployment XML

Example 14-10 shows the pair of <ejb-relationship-role> elements that define a many-to-one bidirectional relationship between Employees and Department. For a unidirectional relationship, you would omit the cmr-field from the appropriate <ejb-relationship-role> element.

Example 14-10 ejb-jar.xml for an EJB 2.1 Bidirectional Many-to-One Relationship

...
<relationships>
    <ejb-relation>
        <ejb-relation-name>Employee-Department</ejb-relation-name>
        <ejb-relationship-role>
            <ejb-relationship-role-name>employees-belongto-dept</ejb-relationship-role-name>
            <multiplicity>Many</multiplicity>
            <relationship-role-source>
                <ejb-name>DepartmentEJB</ejb-name>
            </relationship-role-source>
            <cmr-field>
                <cmr-field-name>dept</cmr-field-name>
            </cmr-field>
        </ejb-relationship-role>
        <ejb-relationship-role>
            <ejb-relationship-role-name>dept-has-employees</ejb-relationship-role-name>
            <multiplicity>One</multiplicity>
            <cascade-delete/>
            <relationship-role-source>
                <ejb-name>LineItemEJB</ejb-name>
            </relationship-role-source>
            <cmr-field>
                <cmr-field-name>employees</cmr-field-name>
                <cmr-field-type>java.util.Collection</cmr-field-type>
            </cmr-field>
        </ejb-relationship-role>
    </ejb-relation>
...
<relationships>