EclipseLink/UserGuide/MOXy/Relationships/Shared Reference/Keys and Foreign Keys/Single Key

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Key API

• XmlID
• XmlIDREF

Single Key

To model non-privately-owned relationships, your "target" objects must have IDs (keys) defined, and your "source" object must use these IDs to map the relationship.

Relationships represented with keys use the @XmlID and @XmlIDREF annotations. Although the JAXB specification requires that the property marked with @XmlID be a String, MOXy JAXB does not enforce this restriction.

In this example, each Employee has one manager but multiple reports.

@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {
    @XmlAttribute
    @XmlID
    private Integer id;
 
    @XmlAttribute
    private String name;
 
    @XmlIDREF
    private Employee manager;
 
    @XmlElement(name="report")
    @XmlIDREF
    private List<Employee> reports;
 
    ...
}

This would produce the following XML:

<company>
    <employee id="1" name="Jane Doe">
        <report>2</report>
        <report>3</report>
    </employee>
    <employee id="2" name="John Smith">
        <manager>1</manager>
    </employee>
    <employee id="3" name="Anne Jones">
        <manager>1</manager>
    </employee>
</company>

The manager and reports elements contain the IDs of the Employee instances they are referencing.

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

...
<java-type name="Employee">
   <java-attributes>
      <xml-attribute java-attribute="id" type="java.lang.Integer" xml-id="true" />
      <xml-attribute java-attribute="name" type="java.lang.String" />
      <xml-element java-attribute="manager" type="mypackage.Employee" xml-idref="true" />
      <xml-element java-attribute="reports" type="mypackage.Employee" container-type="java.util.ArrayList" xml-idref="true" />
   </java-attributes>
</java-type>
...

Because the @XmlIDREF annotation is also compatible with the @XmlList annotation, the Employee object could be modeled as:

@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {
    @XmlID
    @XmlAttribute
    private Integer id;
 
    @XmlAttribute
    private String name;
 
    @XmlIDREF
    private Employee manager;
 
    @XmlIDREF
    @XmlList
    private List<Employee> reports;
 
    ... 
}

This would produce the following XML:

<company>
   <employee id="1" name="Jane Doe">
      <reports>2 3</reports>
   </employee>
   <employee id="2" name="John Smith">
      <manager>1</manager>
   </employee>
   <employee id="3" name="Anne Jones">
      <manager>1</manager>
   </employee>
</company>

Version: 2.2.0
Other versions...

Keys and Foreign Keys	Keys and Foreign Keys	Composite Key
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