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| <td align="left" valign="top"><div class="booktitle">Developing JAXB Applications Using EclipseLink MOXy, |
| <b>Release 2.7</b><br /></font></td> |
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| <div class="sect1"><!-- infolevel="all" infotype="General" --> |
| <h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">Mapping Bidirectional Relationships</font></h1> |
| <p>In order to map bidirectional relationships in EclipseLink MOXy, the back-pointer must be annotated as an <code>@XmlInverseReference</code>. Without this annotation, the cyclic relationship will result in an infinite loop during marshalling.</p> |
| <p><code>@XmlInverseReferences</code> must specify the <code>mappedBy</code> attribute, which indicates the property on the opposite side of the relationship.</p> |
| <p>In <a href="#BABHGBAG">Example 7-11</a>, an <code>Employee</code> has a collection of <code>PhoneNumbers</code>, and each <code>PhoneNumber</code> has a back-pointer back to its <code>Employee</code>:</p> |
| <div class="example"><a id="TLJAX359" name="TLJAX359"></a><a id="sthref135" name="sthref135"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 7-10 Using the @XMlInverseReference Annotation</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| @XmlAccessorType(XmlAccessType.FIELD) |
| public class Employee { |
| private String name; |
| private List<PhoneNumber> phones = new ArrayList<PhoneNumber>(); |
| ... |
| } |
| |
| @XmlAccessorType(XmlAccessType.FIELD) |
| public class PhoneNumber { |
| private String number; |
| <strong>@XmlInverseReference</strong>(mappedBy="phones") |
| private Employee employee; |
| ... |
| } |
| |
| </pre></div> |
| <!-- class="example" --> |
| <p><a href="#BABHGBAG">Example 7-11</a> shows how to define this mapping in EclipseLink's OXM metadata format:</p> |
| <div class="example"><a id="BABHGBAG" name="BABHGBAG"></a><a id="TLJAX360" name="TLJAX360"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 7-11 Sample XML Mapping</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| ... |
| <java-type name="Employee"> |
| <java-attributes> |
| <xml-element java-attribute="name" type="java.lang.String"/> |
| <xml-element java-attribute="phones" type="PhoneNumber" container-type="java.util.ArrayList"/> |
| </java-attributes> |
| </java-type> |
| |
| <java-type name="PhoneNumber"> |
| <java-attributes> |
| <xml-element java-attribute="number" type="java.lang.String"/> |
| <xml-inverse-reference java-attribute="employee" type="Employee" mapped-by="phones" /> |
| </java-attributes> |
| </java-type> |
| ... |
| |
| In addition, when using @XmlInverseReference, it is not necessary to explicitly set the back-pointer in your Java code; EclipseLink will do this for you automatically: |
| </pre></div> |
| <!-- class="example" --> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| Employee emp = new Employee(); |
| emp.setName("Bob Smith"); |
| |
| PhoneNumber p = new PhoneNumber(); |
| p.setNumber("555-1212"); |
| |
| emp.getPhones().add(p); |
| |
| // Not Necessary |
| // p.setEmployee(emp); |
| |
| </pre> |
| <p><code>@XmlInverseReference</code> back-pointers can be used with the following types of mappings:</p> |
| <ul> |
| <li> |
| <p>One-To-One Relationships (see <a href="privately_owned_relations001.htm#BABHAJID">"Mapping Privately Owned One-to-One Relationships"</a>)</p> |
| </li> |
| <li> |
| <p>One-To-Many Relationships (see <a href="privately_owned_relations002.htm#BABGFHAG">"Mapping Privately Owned One-to-Many Relationships"</a>)</p> |
| </li> |
| <li> |
| <p>Single Key Relationships (see <a href="shared_reference_relations002.htm#BABHIHAE">"Mapping Single Key Relationships"</a>)</p> |
| </li> |
| <li> |
| <p>Composite Key Relationships (see <a href="shared_reference_relations004.htm#BABIIBFI">"Mapping Composite Key Relationships"</a>)</p> |
| </li> |
| </ul> |
| <p><code>@XmlInverseReference</code> can be particularly useful when mapping JPA entities to XML (see <a href="runtime003.htm#CACHCHAE">"Using XML Bindings"</a>)</p> |
| <a id="TLJAX361" name="TLJAX361"></a> |
| <div class="sect2"><a id="sthref136" name="sthref136"></a> |
| <h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">See also</font></h2> |
| <p>For more information, see:</p> |
| <ul> |
| <li> |
| <p>Binding JPA Relationships to XML<br /> |
| <code><a href="http://wiki.eclipse.org/EclipseLink/Examples/MOXy/JPA/Relationships">http://wiki.eclipse.org/EclipseLink/Examples/MOXy/JPA/Relationships</a></code></p> |
| </li> |
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