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<title>Entity</title>
 
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<p><a id="BABGBIEE" name="BABGBIEE"></a></p>
<div class="sect2"><!-- infolevel="all" infotype="General" -->
<h1>Entity</h1>
<p><a id="sthref57" name="sthref57"></a><a id="sthref58" name="sthref58"></a><a id="sthref59" name="sthref59"></a><a id="sthref60" name="sthref60"></a>An <span class="bold">Entity</span> is a persistent domain object.</p>
<p>An entity <span class="italic">can be</span>:</p>
<ul>
<li>
<p>Abstract or concrete classes. Entities may also extend non-entity classes as well as entity classes, and non-entity classes may extend entity classes.</p>
</li>
</ul>
<p>An entity <span class="italic">must have</span>:</p>
<ul>
<li>
<p>A no-arg constructor (public or protected); the entity class may have other constructors as well.</p>
</li>
</ul>
<p><a id="sthref61" name="sthref61"></a><a id="sthref62" name="sthref62"></a><a id="sthref63" name="sthref63"></a>Each persistent entity must be mapped to a database table and contain a primary key. Persistent entities are identified by the <code>@Entity</code> annotation.</p>
<p>Use this procedure to add persistence to an existing entity:</p>
<ol start="1">
<li>
<p>Open the Java class in the <span class="gui-object-title">Package Explorer.</span></p>
</li>
<li>
<p>Select the class in the JPA Structure view.</p>
</li>
<li>
<p>In the JPA Details view, click the mapping type hyperlink to access the Mapping Type Selection dialog. In the following figure, clicking <span class="italic">entity</span> invokes the dialog from the JPA Details View.</p>
<div class="figure"><a id="sthref64" name="sthref64"></a>
<p class="titleinfigure">The Mapping Type Hyperlink</p>
<img src="img/mapped_entity_type_link.png" alt="The JPA Details view for an entity showing the mapping type hyperlink." title="The JPA Details view for an entity showing the mapping type hyperlink." /><br /></div>
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<p class="notep1">Tip:</p>
You can also change (or add) persistence for an entity by right-clicking the class in the JPA Structure View and then clicking <span class="bold">Map As &gt; Entity</span>.</td>
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</li>
<li>
<p>Select <span class="bold">Entity</span> from the Mapping Type Selection dialog and then click <span class="bold">OK</span>.</p>
<div class="figure"><a id="sthref65" name="sthref65"></a>
<p class="titleinfigure">The Mapping Type Selection Dialog</p>
<img src="img/mapping_type_selection_entity.png" alt="The Mapping Type selection dialog with Enity selected." title="The Mapping Type selection dialog with Enity selected." /><br /></div>
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<li>
<p>Complete the remaining <a href="ref_persistence_prop_view.htm#BABFAEBB">JPA Details view (for entities)</a>.</p>
</li>
</ol>
<p>&nbsp;</p>
<img src="img/ngrelt.png" alt="Related tasks" title="Related tasks" /><br />
<br />
<a href="task_add_persistence.htm#BABHICAI">Adding persistence to a class</a><br />
<a href="task_additonal_tables.htm#CIHGBIEI">Specifying additional tables</a><br />
<a href="task_inheritance.htm#CIHCCCJD">Specifying entity inheritance</a><br /></div>
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