Many-to-Many Unidirectional Generic
Relationships
Use
A many-to-many generic unidirectional relationship has a field of type java.util.Set with an interface element type or an object element type on one of the sides of the relationship.
In the relational model, there is a generic persistent reference in a join table that logically belongs to the class of the one side of the relationship.
Example
The class example.jdo.Employee contains field set with element type example.jdo.SomeInterface. There is a join table TMP_JOIN with the foreign key column EMPLOYEEcorresponding to the primary key column EMPID in table TMP_EMPLOYEE. The join table also contains the generic persistent reference that consists of the columns REF1DISC and REF1 for the discriminator and the reference.
The XML metadata has the following contents:
<jdo>
<package name="example.jdo">
<class name="Employee" identity-type="application" objectid-class="Employee$Id">
<field name="empid" persistence-modifier="persistent" primary-key="true"/>
<field name="set" persistence-modifier="persistent"
embedded="false" default-fetch-group="false">
<collection element-type="employee.jdo.SomeInterface" embedded-element="false"/>
</field>
</class>
</package>
</jdo>
<map version="1.0">
<package name="example.jdo">
<class name="Employee">
<field name="empid">
<column name="EMPID" table="TMP_EMPLOYEE"/>
</field>
<relationship-field name="set" multiplicity="many" join-table="true">
<foreign-key name="JOIN_TO_EMPLOYEE"
foreign-key-table="TMP_JOIN" primary-key-table="TMP_EMPLOYEE">
<column-pair foreign-key-column="EMPLOYEE" primary-key-column="EMPID"/>
</foreign-key>
<discriminator>
<column name="REF1DISC" table="TMP_JOIN"/>
</discriminator>
<reference>
<column name="REF1" table="TMP_JOIN"/>
</reference>
</relationship-field>
</class>
</map>