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Difference between revisions of "EclipseLink/UserGuide/MOXy/Relationships/Privately Owned/One-to-One"

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</source>
 
</source>
  
==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 <tt>xsi:nil</tt> to represent a null value (e.g. <tt><first-name xsi:nil="true"/></tt>), or it might simply use an empty element (e.g. <tt><first-name></first-name></tt>).  On the Java side, you may want to specify exactly how a null value should be written to XML (<tt>nil</tt> 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:
 
 
<source lang="xml">
 
<?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>
 
</source>
 
 
An example instance document might look like:
 
 
<source lang="xml">
 
<customer>
 
  <id/>
 
  <name>Jon Smith</name>
 
  <account-number xsi:nil="true"/>
 
</customer>
 
</source>
 
 
For this example, we would like:
 
 
* Empty <tt>id</tt> tags to correspond to <tt>null</tt> in Java
 
* Empty <tt>name</tt> tags to correspond to "" (empty string) in Java (this is EclipseLink's default null-handling behavior)
 
* A <tt>nil</tt> <tt>account-number</tt> to correspond to <tt>null</tt> in Java
 
 
To achieve this behavior in EclipseLink, our mappings can be defined using annotations as follows:
 
 
<source lang="java">
 
import org.eclipse.persistence.oxm.annotations.XmlNullPolicy;
 
import org.eclipse.persistence.oxm.annotations.XmlMarshalNullRepresentation;
 
 
@XmlRootElement
 
@XmlAccessorType(XmlAccessType.FIELD)
 
public class Customer {
 
  private String id;
 
 
  private String name;
 
 
  @XmlElement(name="account-number")
 
  @XmlNullPolicy(xsiNilRepresentNull="true" nullRepresentationForXml=XmlMarshalNullRepresentation.XSI_NIL)
 
  private String accountNumber;
 
 
  ...
 
}
 
</source>
 
 
Here, we have specified that <tt>xsi:nil</tt> in XML should represent <tt>null</tt> in Java, and conversely, that <tt>null</tt> in Java should be represented by <tt>xsi:nil</tt> in XML.
 
  
 
{{EclipseLink_MOXy
 
{{EclipseLink_MOXy

Revision as of 09:47, 6 January 2011

EclipseLink MOXy

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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
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
   @XmlElement(name="phone-number")
   private PhoneNumber phoneNumber;
 
   ...
}
 
@XmlAccessorType(XmlAccessType.FIELD)
public class PhoneNumber {
   @XmlElement(name="area-code")
   private Integer areaCode;
 
   private Integer number;
 
   private Integer extension;
 
   ...
}

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
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
   @XmlPath(".")
   private PhoneNumber phoneNumber;
 
   ...
}
 
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>


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