Mapping Privately Owned One-to-Many Relationships

This section illustrates how to map one-to-many relationships with EclipseLink.

The schema in Example 6-8 a typical one-to-many (1:M) relationship between Customer and PhoneNumber, as shown in Figure 6-2.

Example 6-8 Sample XML Mapping

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 
   <xsd:element name="customer" type="customer-type"/>
 
   <xsd:complexType name="customer-type">
      <xsd:sequence>
         <xsd:element name="first-name" type="xsd:string"/>
         <xsd:element name="last-name" type="xsd:string"/>
         <xsd:element name="phone-number" type="phone-type" minOccurs="0" maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
 
   <xsd:complexType name="phone-type">
      <xsd:sequence>
         <xsd:attribute name="type" type="xsd:string"/>
         <xsd:element name="number" type="xsd:int"/>
      </xsd:sequence>
   </xsd:complexType>
 
</xsd:schema>

Figure 6-2 One-to-many Relationship

Description of "Figure 6-2 One-to-many Relationship"

Mapping to Elements

Example 6-9 shows how to annotate your Java class to obtain this mapping with EclipseLink. The standard JAXB @XmlElement annotation, when used on a Collection or array field, can achieve this.

Example 6-9 Using the @XmlElement Annotation

package example;
 
import jakarta.xml.bind.annotation.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
   @XmlElement(name="first-name")
   private String firstName;
   @XmlElement(name="last-name")
   private String lastName;
   @XmlElement(name="phone-number")
   private List<PhoneNumber> phoneNumbers;
 
   ...
}
 
package example;
 
import jakarta.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.*;
 
@XmlAccessorType(XmlAccessType.FIELD)
public class PhoneNumber {
   @XmlAttribute
   private String type;
   private Integer number;
 
   ...
}

Example 6-10 shows how to define your mapping information in EclipseLink's OXM metadata format.

Example 6-10 Sample XML Mapping

...
<java-type name="Customer">
   <xml-root-element name="customer"/>
   <java-attributes>
      <xml-element java-attribute="firstName" name="first-name" type="java.lang.String"/>
      <xml-element java-attribute="lastName" name="last-name" type="java.lang.String"/>
      <xml-element java-attribute="phoneNumbers" name="phone-number" type="PhoneNumber" container-type="java.util.ArrayList"/>
   </java-attributes>
</java-type>
 
<java-type name="PhoneNumber">
   <java-attributes>
      <xml-attribute java-attribute="type" type="java.lang.String"/>
      <xml-value java-attribute="number" type="java.lang.Integer"/>
   </java-attributes>
</java-type>
...

Grouping Elements using the @XmlElementWrapper Annotation

To make the elements of the Collection appear inside a grouping element, you can use @XmlElementWrapper:

Example 6-11 Using the @XmlElementWrapper Annotation

package example;
 
import jakarta.xml.bind.annotation.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
   @XmlElement(name = "phone-number")
   @XmlElementWrapper(name="phone-numbers")
   private List<PhoneNumber> phoneNumbers;
 
   ...
}

This will produce the following XML:

<customer>
   <first-name>Bob</first-name>
   <last-name>Smith</last-name>
   <phone-numbers>
      <phone-number type="Home">
         <number>5559827222</number>
      </phone-number>
      <phone-number type="Work">
         <number>5558872216</number>
      </phone-number>
   </phone-numbers>
</customer>