Question

I am using Hibernate and RESTeasy, i try to avoid a cycle with these entities, as i have a OneToMany (ManyToOne) bidirectionnal relation between Artiste and Oeuvre entities :

Oeuvre.java

import javax.persistence.*;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlInverseReference;

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@XmlRootElement(name = "oeuvre")
public abstract class Oeuvre {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @Embedded
    private Dimension dimension;

    @XmlElement(defaultValue = "true")
    private boolean hasBeenReproduced;

    @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    @JoinColumn(name = "artiste_id")
    @XmlIDREF
    private Artiste artiste;

    @XmlElement
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    // @XmlTransient
    @XmlInverseReference(mappedBy = "oeuvres")
    public Artiste getArtiste() {
        return artiste;
    }

    public void setArtiste(Artiste artiste) {
        this.artiste = artiste;
        artiste.addOeuvre(this);
    }

}

Personne.java

import javax.persistence.*;
import javax.xml.bind.annotation.XmlID;

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Personne {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    @XmlID
    private int id;

}

Artiste.java

import java.util.*;
import javax.persistence.*;
import javax.xml.bind.annotation.*;

@Entity
@XmlRootElement(name = "artiste")
public class Artiste extends Personne {

    private String bibliographie;

    @OneToMany(mappedBy = "artiste", orphanRemoval = true, cascade = {
            CascadeType.PERSIST, CascadeType.REMOVE })
    private List<Oeuvre> oeuvres = new ArrayList<Oeuvre>();

    @XmlElement
    public List<Oeuvre> getOeuvres() {
        return oeuvres;
    }

    public void setOeuvres(List<Oeuvre> oeuvres) {
        this.oeuvres = oeuvres;
    }

}

So i decided to use MOXy,

Here is my POM

<repository>
        <id>EclipseLink</id>
        <url>http://download.eclipse.org/rt/eclipselink/maven.repo</url>
</repository>
<dependency>
       <groupId>org.eclipse.persistence</groupId>
       <artifactId>org.eclipse.persistence.moxy </artifactId>
       <version>2.3.2</version>     
    </dependency>

nb : i would like to only have org.eclipse.persistence.moxy-2.3.2.jar as i am using hibernate (i don’t want eclipseLink), but i also have 3 other jars (including the core)

Then i put a jaxb.properties file in the package of my entities :

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

And added @XmlInverseReference(mappedBy=”oeuvres”) to getArtiste() instead od @XmlTranscient
==> i don’t have cycle anymore (like xmlTranscient) but i still don’t have any back pointer.

Then i added @XmlID & @XmlIDREF, the id of the artist is now represented in the xml result of a work of art BUT it doesn’t have the good value (0 but shoud be something else)

<Oeuvre>
  <hasBeenReproduced>false</hasBeenReproduced>
  <artiste>0</artiste>
  <year>2010</year>
  <id>2</id>
  <titre>La joconde</titre>
</Oeuvre>

What am i doing wrong ? Thx in advance

EDIT :

Ok i have the following output using @XmlInverseReference when i marshall an “Artiste” Object :

<artiste>
  <id>1</id>
  <nom>a</nom>
  <prenom>b</prenom>
  <oeuvres>
     <hasBeenReproduced>false</hasBeenReproduced>
     <year>2010</year>
     <id>25</id>
     <titre>La joconde</titre>
  </oeuvres>
</artiste>    

According to your example this is the correct behaviour.
So if i understand well, it’s not possible to have a reference of the artiste id in the “Oeuvre” output (given above). We can’t retrieve the artist from a work of art.
In my case i don’t have to use @XmlID ?

Thx for your complete answer Blaise Doughan, it is much appreciated

Answer 1

Note: I’m the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

Below is a simplified example of how to use MOXy’s @XmlInverseReference extension.

Foo

Foo is the root object for this example.

package forum13957068;

import java.util.List;

import javax.xml.bind.annotation.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {

    String fooProp;

    @XmlElement(name="bar")
    List<Bar> bars;

}

Bar

Bar is a child object. We use the @XmlInverseReference annotation to populate the foo field with a reference to the parent object.

package forum13957068;

import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlInverseReference;

@XmlAccessorType(XmlAccessType.FIELD)
public class Bar {

    private String barProp;

    @XmlInverseReference(mappedBy="bars")
    Foo foo;

}

jaxb.properties

To specify MOXy as your JAXB provider you need to include a file called jaxb.properties with the following entry:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

input.xml

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <fooProp>A</fooProp>
    <bar>
        <barProp>B</barProp>
    </bar>
    <bar>
        <barProp>B</barProp>
    </bar>
</foo>

Demo

The following demo code will unmarshal the XML, check the back pointer and then marshal the objects back to XML.

package forum13957068;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Foo.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum13957068/input.xml");
        Foo foo = (Foo) unmarshaller.unmarshal(xml);

        for(Bar bar : foo.bars) {
            System.out.println(bar.foo == foo);
        }

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(foo, System.out);
    }

}

Output

Below is the output of running the demo code. Node how the back pointer is populated correctly.

true
true
<?xml version="1.0" encoding="UTF-8"?>
<foo>
   <fooProp>A</fooProp>
   <bar>
      <barProp>B</barProp>
   </bar>
   <bar>
      <barProp>C</barProp>
   </bar>
</foo>

---

MOXy and Maven

You can use the following in your pom.xml file to pull in MOXy.

<dependencies>
    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>org.eclipse.persistence.moxy</artifactId>
        <version>2.4.1</version>
    </dependency>
</dependencies>
<repositories>
    <repository>
        <id>EclipseLink Repo</id>
        <url>http://download.eclipse.org/rt/eclipselink/maven.repo</url>
    </repository>
</repositories>

For some example POM files that pull in MOXy check out the examples I have hosted on GitHub:

• https://github.com/bdoughan

---

UPDATE

According to your example this is the correct behaviour. So if i
understand well, it’s not possible to have a reference of the artiste
id in the “Oeuvre” output (given above). We can’t retrieve the artist
from a work of art. In my case i don’t have to use @XmlID ?

Below I’ve provided an alternate mapping that uses @XmlID/@XmlIDREF instead of @XmlInverseReference.

Foo

package forum13957068;

import java.util.List;
import javax.xml.bind.annotation.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {

    @XmlID
    String id;

    String fooProp;

    @XmlElement(name="bar")
    List<Bar> bars;

}

Bar

package forum13957068;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Bar {

    private String barProp;

    @XmlIDREF
    Foo foo;

}

input.xml

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <id>1</id>
    <fooProp>A</fooProp>
    <bar>
        <foo>1</foo>
        <barProp>B</barProp>
    </bar>
    <bar>
        <foo>1</foo>
        <barProp>B</barProp>
    </bar>
</foo>

For More Information

• http://blog.bdoughan.com/2010/10/jaxb-and-shared-references-xmlid-and.html