EclipseLink/UserGuide/MOXy/Relationships/Bidirectional Relationships

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Bidirectional Relationships

In order to map bidirectional relationships in EclipseLink MOXy, the back-pointer must be annotated as an @XmlInverseReference. Without this annotation, the cyclic relationship will result in an infinite loop during marshalling.

@XmlInverseReferences must specify the mappedBy attribute, which indicates the property on the opposite side of the relationship.


The following example shows how to define this mapping in EclipseLink's OXM metadata format:

...
<java-type name="Customer">
   <xml-root-element name="customer"/>
   <java-attributes>
      <xml-element java-attribute="phoneNumber" name="phone-number" type="PhoneNumber"/>
   </java-attributes>
</java-type>
 
<java-type name="PhoneNumber">
   <java-attributes>
      <xml-value java-attribute="areaCode" name="area-code" type="java.lang.Integer"/>
      <xml-value java-attribute="number" type="java.lang.Integer"/>
      <xml-value java-attribute="extension" type="java.lang.Integer"/>
   </java-attributes>
</java-type>
...


In this example, an Employee has a collection of PhoneNumbers, and each PhoneNumber has a back-pointer back to its Employee:

@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {
   private String name;
   private List<PhoneNumber> phones = new ArrayList<PhoneNumber>();
   ...
}
 
@XmlAccessorType(XmlAccessType.FIELD)
public class PhoneNumber {
   private String number;
   @XmlInverseReference(mappedBy="phones")
   private Employee employee;
   ...
}

In addition, when using @XmlInverseReference, it is not necessary to explicitly set the back-pointer in your Java code; EclipseLink will do this for you automatically:

Employee emp = new Employee();
emp.setName("Bob Smith");
 
PhoneNumber p = new PhoneNumber();
p.setNumber("555-1212");
 
emp.getPhones().add(p);
 
// Not Necessary
// p.setEmployee(emp);


@XmlInverseReference back-pointers can be used with the following types of mappings:


@XmlInverseReference can be particularly useful when mapping JPA entities to XML. For an example, please see Binding JPA Relationships to XML.


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