EclipseLink/UserGuide/MOXy/Relationships/Privately Owned/One-to-One

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Contents


Mapping One-to-One Relationships

This section demonstrates several ways to map a one-to-one relationship between objects.

Mapping to a Complex Type

Given the XML schema in this example, the figure below illustrates a one-to-one relationship between two complex types.

<?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:element name="address" type="address-type"/>
   </xsd:complexType>
 
   <xsd:complexType name="phone-type">
      <xsd:element name="area-code" type="xsd:int"/>
      <xsd:element name="number" type="xsd:int"/>
      <xsd:element name="extension" type="xsd:int"/>
   </xsd:complexType>
 
</xsd:schema>

Onetoone.png

The following example shows how to annotate your Java class to obtain this mapping with EclipseLink. All that is needed is the standard JAXB @XmlElement annotation.

@XmlRootElement
public class Customer {
   @XmlElement(name="phone-number")
   private PhoneNumber phoneNumber;
 
   public void setPhoneNumber(PhoneNumber value) {
      this.phoneNumber = value;
   }
}
 
public class PhoneNumber {
   @XmlElement(name="area-code")
   private Integer areaCode;
 
   private Integer number;
 
   private Integer extension;
 
   public void setAreaCode(Integer value) {
      this.areaCode = value;
   }
   ...
}

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

...
<java-type name="Customer">
   <xml-root-element name="customer"/>
   <java-attributes>
      <xml-element java-attribute="phoneNumber" name="phone-number" type="PhoneNumber"/>
   </java-attributes>
</java-type>
 
<java-type name="PhoneNumber">
   <java-attributes>
      <xml-value java-attribute="areaCode" name="area-code" type="java.lang.Integer"/>
      <xml-value java-attribute="number" type="java.lang.Integer"/>
      <xml-value java-attribute="extension" type="java.lang.Integer"/>
   </java-attributes>
</java-type>
...

"Self" Mappings

EclipseLink allows you to configure your one-to-one mapping such that the data from the target object will appear inside the source object's XML element. Using the example above, this means that the "PhoneNumber" information would appear directly under the "customer" element, and not wrapped in a "phone-number" element. This is referred to as a "self" mapping, and is achieved by setting the target object's XPath to "." (dot). The following example demonstrates a self mapping declared in annotations.

@XmlRootElement
public class Customer {
   @XmlPath(".")
   private PhoneNumber phoneNumber;
 
   public void setPhoneNumber(PhoneNumber value) {
      this.phoneNumber = value;
   }
   ...
}
 
public class PhoneNumber {
   ...
}

The example below shows a self mapping defined on EclipseLink OXM metadata format.

...
<java-type name="Customer">
   <xml-root-element name="customer"/>
   <java-attributes>
      <xml-element java-attribute="phoneNumber" type="PhoneNumber" xml-path="."/>
   </java-attributes>
</java-type>
 
<java-type name="PhoneNumber">
   ...
</java-type>
...

Using a self mapping, the following XML will be produced:

<customer>
   <area-code>613</area-code>
   <number>2883000</number>
   <extension>1547</extension>
</customer>

Working with Null Values

Eclipselink offers several ways to configure its handling of null values in both Java and XML. For example, your XML may use xsi:nil to represent a null value (e.g. <first-name xsi:nil="true"/>), or it might simply use an empty element (e.g. <first-name></first-name>). On the Java side, you may want to specify exactly how a null value should be written to XML (nil or empty node). You can even specify an "isSet" method, to differentiate between values that were explicitly set to null versus values which are null due to being unset.

Consider the following schema:

<?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:element name="id" type="xsd:string"/>
      <xsd:element name="name" type="xsd:string"/>
      <xsd:element name="account-number" type="xsd:string" nillable="true"/>
   </xsd:complexType>
 
</xsd:schema>

An example instance document might look like:

<customer>
   <id/>
   <name>Jon Smith</name>
   <account-number xsi:nil="true"/>
</customer>

For this example, we would like:

  • Empty id tags to correspond to null in Java
  • Empty name tags to correspond to "" (empty string) in Java (this is EclipseLink's default null-handling behavior)
  • A nil account-number to correspond to null in Java

To achieve this behavior in EclipseLink, our mappings can be defined using annotations as follows:

import org.eclipse.persistence.oxm.annotations.XmlNullPolicy;
import org.eclipse.persistence.oxm.annotations.XmlMarshalNullRepresentation;
 
@XmlRootElement
public class Customer {
   @XmlElement
   private String id;
 
   @XmlElement
   private String name;
 
   @XmlElement(name="account-number")
   @XmlNullPolicy(xsiNilRepresentNull="true" nullRepresentationForXml=XmlMarshalNullRepresentation.XSI_NIL)
   public String accountNumber;
 
   public void setId(String value) {
      this.id = value;
   }
   ...
}

Here, we have specified that xsi:nil in XML should represent null in Java, and conversely, that null in Java should be represented by xsi:nil in XML.

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Version: 2.2.0 DRAFT
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