Bidirectional relations are an essential part of data modeling. Chapter 12, Mapping Metadata in the JPA Overview explains how to use the mappedBy annotation attribute to form bidirectional relations that also share datastore storage in JPA. Chapter 15, Mapping Metadata in the JDO Overview explains how to do the same thing using the the mapped-by mapping attribute in JDO.

Kodo also allows you to define purely logical bidirectional relations. The org.apache.openjpa.persistence.InverseLogical annotation names a logical inverse in JPA metadata. The inverse-logical field extension names a logical inverse in JDO metadata.

import org.apache.openjpa.persistence.*;

@Entity
public class Magazine
{
    @OneToOne
    private Photograph coverPhoto;
    
    ...
}

@Entity
public class Photograph
{
    @OneToOne
    @InverseLogical("coverPhoto")
    private Magazine mag;
    
    ...
}

<class name="Magazine">
    <field name="coverPhoto"/>
    ...
</class>
<class name="Photograph">
    <field name="mag">
        <extension vendor-name="kodo" key="inverse-logical" value="coverPhoto"/>
    </field>
    ...
</class>

Java does not provide any native facilities to ensure that both sides of a bidirectional relation remain consistent. Whenever you set one side of the relation, you must manually set the other side as well.

By default, Kodo behaves the same way. Kodo does not automatically propagate changes from one field in bidirectional relation to the other field. This is in keeping with the philosophy of transparency, and also provides higher performance, as Kodo does not need to analyze your object graph to correct inconsistent relations.

If convenience is more important to you than strict transparency, however, you can enable inverse relation management in Kodo. Set the kodo.InverseManager plugin property to true for standard management. Under this setting, Kodo detects changes to either side of a bidirectional relation (logical or physical), and automatically sets the other side appropriately on flush.

<property name="kodo.InverseManager" value="true"/>

kodo.InverseManager: true

The inverse manager has options to log a warning or throw an exception when it detects an inconsistent bidirectional relation, rather than correcting it. To use these modes, set the manager's Action property to warn or exception, respectively.

By default, Kodo excludes large result set fields from management. You can force large result set fields to be included by setting the ManageLRS plugin property to true.

<property name="kodo.InverseManager" value="true(Action=warn)"/>

kodo.InverseManager: true(Action=warn)