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Difference between revisions of "EclipseLink/UserGuide/MOXy/Relationships/Bidirectional Relationships"

Line 39: Line 39:
 
   <java-attributes>
 
   <java-attributes>
 
       <xml-element java-attribute="name" type="java.lang.String"/>
 
       <xml-element java-attribute="name" type="java.lang.String"/>
       <xml-element java-attribute="name" type="java.lang.String"/>
+
       <xml-element java-attribute="phones" type="PhoneNumber" container-type="java.util.ArrayList"/>
 
+
 
   </java-attributes>
 
   </java-attributes>
 
</java-type>
 
</java-type>

Revision as of 15:31, 26 April 2011


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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.


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;
   ...
}


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

...
<java-type name="Employee">
   <java-attributes>
      <xml-element java-attribute="name" type="java.lang.String"/>
      <xml-element java-attribute="phones" type="PhoneNumber" container-type="java.util.ArrayList"/>
   </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 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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