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

EclipseLink MOXy

Mapping Composite Key Relationships

If the objects that you want to map have multi-part keys (i.e., a combination of fields that determines uniqueness), you can use EclipseLink's @XmlKey and @XmlJoinNodes to set up this relationship.

In this example, each Employee has one manager but multiple reports, and Employees are uniquely identified by the combination of their id and name fields.

@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {
    @XmlID
    @XmlAttribute
    private Integer id;
 
    @XmlKey
    @XmlAttribute
    private String name;
 
    @XmlJoinNodes( {
        @XmlJoinNode(xmlPath = "manager/@id", referencedXmlPath = "@id"),
        @XmlJoinNode(xmlPath = "manager/@name", referencedXmlPath = "@name") })
    public Employee manager;
 
    @XmlJoinNodes( {
        @XmlJoinNode(xmlPath = "report/@id", referencedXmlPath = "@id"),
        @XmlJoinNode(xmlPath = "report/@name", referencedXmlPath = "@name") })
    public List<Employee> reports = new ArrayList<Employee>();
 
    ...
}

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>
...

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.


Using @XmlList

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>

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Version: 2.2.0 DRAFT
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