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<title>Specifying Inheritance | EclipseLink 2.7 EclipseLink MOXy</title>
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<div class="sect1"><!-- infolevel="all" infotype="General" -->
<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">Specifying Inheritance</font></h1>
<p>EclipseLink MOXy provides several ways to represent your inheritance hierarchy in XML:</p>
<ul>
<li>
<p><a href="#BABGHADJ">Using xsi:type</a></p>
</li>
<li>
<p><a href="#BABIICIB">Using Substitution Groups</a></p>
</li>
<li>
<p><a href="#BABHIBJJ">Using @XmlDiscriminatorNode/@XmlDiscriminatorValue</a></p>
</li>
</ul>
<a id="BABGHADJ" name="BABGHADJ"></a><a id="TLJAX206" name="TLJAX206"></a>
<div class="sect2">
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Using xsi:type</font></h2>
<p>By default, EclipseLink will use the <code>xsi:type</code> attribute to represent inheritance in XML.</p>
<p>In this example an abstract super class (<strong>ContactInfo</strong>) contains all types of contact information. <strong>Address</strong> and <strong>PhoneNumber</strong> are the concrete implementations of <strong>ContactInfo</strong>.</p>
<div class="example"><a id="CIHCJDHH" name="CIHCJDHH"></a><a id="TLJAX207" name="TLJAX207"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-12 Sample Java Classes</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
public abstract class ContactInfo {
}
public class Address extends ContactInfo {
private String street;
...
}
public class PhoneNumber extends ContactInfo {
private String number;
...
}
</pre></div>
<!-- class="example" -->
<p>Because the <strong>Customer</strong> object can have different types of contact information, its property refers to the superclass.</p>
<pre xml:space="preserve" class="oac_no_warn">
@XmlRootElement
public class Customer {
private ContactInfo contactInfo;
...
}
</pre>
<p>Marshalling an example <strong>Customer</strong> would produce the following XML:</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;contactInfo
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
<strong>xsi:type="address"</strong>&gt;
&lt;street&gt;323 Main Street&lt;/street&gt;
&lt;/contactInfo&gt;
&lt;/customer&gt;
</pre>
<p>Note the <code>xsi:type</code> attribute on the <code>contactInfo</code> element.</p>
</div>
<!-- class="sect2" -->
<a id="BABIICIB" name="BABIICIB"></a><a id="TLJAX208" name="TLJAX208"></a>
<div class="sect2">
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Using Substitution Groups</font></h2>
<p>Another way to model inheritance in XML is through XML Schema's substitution groups functionality. Using this approach, the element name <em>itself</em> determines which subclass to use.</p>
<p>Taking the same <a href="#CIHCJDHH">Example 3-12</a>, we will add <code>@XmlRootElement</code> annotations to each of the subclasses, which will act as the inheritance indicator.</p>
<div class="example"><a id="CIHJCCEE" name="CIHJCCEE"></a><a id="TLJAX209" name="TLJAX209"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-13 Using @XmlRootElement Annotation</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
public abstract class ContactInfo {
}
<strong>@XmlRootElement</strong>
public class Address extends ContactInfo {
private String street;
...
}
<strong>@XmlRootElement</strong>
public class PhoneNumber extends ContactInfo {
private String number;
...
}
</pre></div>
<!-- class="example" -->
<p>Using this approach, marshalling an example <strong>Customer</strong> would produce the following XML:</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;address&gt;
&lt;street&gt;323 Main Street&lt;/street&gt;
&lt;/address&gt;
&lt;/customer&gt;
</pre>
<p>Note that the <strong>Address</strong> object is marshalled to the <code>address</code> element.</p>
</div>
<!-- class="sect2" -->
<a id="BABHIBJJ" name="BABHIBJJ"></a><a id="TLJAX210" name="TLJAX210"></a>
<div class="sect2">
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Using @XmlDiscriminatorNode/@XmlDiscriminatorValue</font></h2>
<p>You can also use the MOXY-specific <code>@XmlDiscriminatorNode</code> and <code>@XmlDiscriminatorValue</code> annotations (introduced in EclipseLink 2.2) to represent inheritance. With this approach, you can select the attribute to represent the subtype.</p>
<p>Using <a href="#CIHJCCEE">Example 3-13</a>, the <strong>ContactInfo</strong> class uses the <code>@XmlDiscriminatorNod</code>e annotation to specify the XML attribute (classifier) that will hold the subclass indicator. <strong>Address</strong> and <strong>PhoneNumber</strong> are annotated with <strong>@XmlDiscriminatorValue</strong>, indicating that class' indicator name (<code>address-classifier</code> and <code>phone-number-classifier</code>).</p>
<div class="example"><a id="CIHGABAC" name="CIHGABAC"></a><a id="TLJAX211" name="TLJAX211"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-14 Using the @XmlDiscriminatorNode and @XmlDiscriminatorValue Annotations</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
<strong>@XmlDiscriminatorNode</strong>("@classifier")
public abstract class ContactInfo {
}
<strong>@XmlDiscriminatorValue</strong>("address-classifier")
public class Address extends ContactInfo {
private String street;
...
}
<strong>@XmlDiscriminatorValue</strong>("phone-number-classifier")
public class PhoneNumber extends ContactInfo {
private String number;
...
}
</pre></div>
<!-- class="example" -->
<p><a href="#CIHGABAC">Example 3-14</a> produces the following XML:</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;contactInfo classifier="address-classifier"&gt;
&lt;street&gt;323 Main Street&lt;/street&gt;
&lt;/contactInfo&gt;
&lt;/customer&gt;
</pre>
<p>Notice that <strong>Address</strong> is marshalled to the <code>contactInfo</code> element. Its classifier attribute contains the discriminator node value <code>address-classifier</code>.</p>
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