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EclipseLink/UserGuide/MOXy/Relationships/Bidirectional Relationships
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Key API
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-element java-attribute="number" type="java.lang.String"/> <xml-inverse-reference java-attribute="employee" type="Employee" mapped-by="phones" /> </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:
- One-To-One Relationships
- One-To-Many Relationships
- Single Key Relationships
- Composite Key Relationships
@XmlInverseReference can be particularly useful when mapping JPA entities to XML. For an example, please see Binding JPA Relationships to XML.