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Difference between revisions of "EclipseLink/UserGuide/MOXy/Relationships/Bidirectional Relationships"
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= Bidirectional Relationships = | = Bidirectional Relationships = | ||
− | In order to map bidirectional relationships in EclipseLink MOXy, | + | 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. | '''@XmlInverseReferences''' must specify the '''mappedBy''' attribute, which indicates the property on the opposite side of the relationship. | ||
Line 30: | Line 30: | ||
</source> | </source> | ||
+ | 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: | ||
+ | <source lang="java"> | ||
+ | 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); | ||
+ | </source> | ||
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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; ... }
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);
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; }