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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, one of the properties 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; ... }
When binding JPA entities to XML, there are MOXy extensions will help you map a bidirectional relationship.
In this sample model, notice that Customer has a relationship to Address, and Address has a relationship back to Customer. In JPA, one direction of the relationship is mapped (the customer property on Address); the other direction specifies a mapping to leverage.
Sample Model
import javax.persistence.*; @Entity public class Customer { @Id private long id; @OneToOne(mappedBy="customer", cascade={CascadeType.ALL}) private Address address; } import javax.persistence.*; @Entity public class Address implements Serializable { @Id private long id; @MapsId @OneToOne @JoinColumn(name="ID") private Customer customer; }
To marshal these objects to XML, mark one direction @XmlTransient' to prevent a JAXB infinite loop during marshalling. Normally, during unmarshalling (from XML-to-object), you are responsible for populating the back pointer
import javax.persistence.*; import javax.xml.bind.annotation.*; @Entity public class Address implements Serializable { @Id private long id; @OneToOne @JoinColumn(name="ID") @MapsId @XmlTransient private Customer customer; }
@XMLInverseReference
With the @XmlInverseReference annotation, MOXy will populate the back pointer automatically. In this sample, notice that the @XmlInverseReference annotation leverages the same "mappedBy" concept.
import javax.persistence.*; import org.eclipse.persistence.oxm.annotations.*; @Entity public class Address implements Serializable { @Id private long id; @OneToOne @JoinColumn(name="ID") @MapsId @XmlInverseReference(mappedBy="address") private Customer customer; }