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<title>Specifying entity inheritance</title>
 
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<p><a id="CIHCCCJD" name="CIHCCCJD"></a></p>
<div class="sect1"><!-- infolevel="all" infotype="General" -->
<h1>Specifying entity inheritance</h1>
<p><a id="sthref80" name="sthref80"></a><a id="sthref81" name="sthref81"></a>An entity may inherit properties from other entities. You can specify a specific strategy to use for inheritance.</p>
<p>Use this procedure to specify inheritance (<code>@Inheritance)</code> for an existing entity (<code>@Entity</code>):</p>
<ol start="1">
<li>
<p>Select the entity in the <span class="gui-object-title">Package Explorer</span>.</p>
</li>
<li>
<p>In the <span class="gui-object-title">JPA Details</span> view, select the <span class="gui-object-action">Inheritance</span> information.</p>
<div class="figure"><a id="sthref82" name="sthref82"></a>
<p class="titleinfigure">Specifying Inheritance</p>
<img src="img/inheritance_tab.png" alt="Selecting the Inheritance area on the JPA Details view." title="Selecting the Inheritance area on the JPA Details view." /><br /></div>
<!-- class="figure" --></li>
<li>
<p>In the <span class="bold">Strategy</span> list, select one of the following the inheritance strategies:</p>
<ul>
<li>
<p>A single table (default)</p>
</li>
<li>
<p>Joined table</p>
</li>
<li>
<p>One table per class</p>
</li>
</ul>
</li>
<li>
<p>Use the following table to complete the remaining fields on the tab. See <a href="reference012.htm#CACFHGHE">"Inheritance information"</a> for additional details.</p>
<div class="inftblruleinformal">
<table class="RuleInformal" title="This table describes the options on the Persistence Properties view, Inheritance tab." summary="This table describes the options on the Persistence Properties view, Inheritance tab." dir="ltr" border="1" width="100%" frame="border" rules="all" cellpadding="3" cellspacing="0">
<thead>
<tr align="left" valign="top">
<th align="left" valign="bottom" id="r1c1-t14">Property</th>
<th align="left" valign="bottom" id="r1c2-t14">Description</th>
<th align="left" valign="bottom" id="r1c3-t14">Default</th>
</tr>
</thead>
<tbody>
<tr align="left" valign="top">
<td align="left" id="r2c1-t14" headers="r1c1-t14"><a id="sthref83" name="sthref83"></a><a id="sthref84" name="sthref84"></a>Discriminator Column</td>
<td align="left" headers="r2c1-t14 r1c2-t14">Name of the discriminator column when using a <span class="bold">Single</span> or <span class="bold">Joined</span> inheritance strategy.
<p>This field corresponds to the <code>@DiscriminatorColumn</code> annotation.</p>
</td>
<td align="left" headers="r2c1-t14 r1c3-t14"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r3c1-t14" headers="r1c1-t14">Discriminator Type</td>
<td align="left" headers="r3c1-t14 r1c2-t14">Set the discriminator type to <code>Char</code> or <code>Integer</code> (instead of its default: <code>String</code>). The <span class="bold">Discriminator Value</span> must conform to this type.</td>
<td align="left" headers="r3c1-t14 r1c3-t14">String</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r4c1-t14" headers="r1c1-t14"><a id="sthref85" name="sthref85"></a><a id="sthref86" name="sthref86"></a>Discriminator Value</td>
<td align="left" headers="r4c1-t14 r1c2-t14">Specify the discriminator value used to differentiate an entity in this inheritance hierarchy. The value must conform to the specified <span class="bold">Discriminator Type</span>.
<p>This field corresponds to the <code>@DiscriminatorValue</code> annotation.</p>
</td>
<td align="left" headers="r4c1-t14 r1c3-t14"><br /></td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r5c1-t14" headers="r1c1-t14">Override Default</td>
<td align="left" headers="r5c1-t14 r1c2-t14">Use this field to specify custom primary key join columns.
<p>This field corresponds to the <code>@PrimaryKeyJoinClumn</code> annotation.</p>
</td>
<td align="left" headers="r5c1-t14 r1c3-t14"><br /></td>
</tr>
</tbody>
</table>
<br /></div>
<!-- class="inftblruleinformal" --></li>
</ol>
<p>Eclipse adds the following annotations the entity field:</p>
<pre xml:space="preserve" class="oac_no_warn">
@Inheritance(strategy=InheritanceType.<span class="italic">&lt;INHERITANCE_STRATEGY&gt;</span>)
@DiscriminatorColumn(name="<span class="italic">&lt;DISCRIMINATOR_COLUMN&gt;</span>",
    discriminatorType=<span class="italic">&lt;DISCRIMINATOR_TYPE&gt;</span>)
@DiscriminatorValue(value-"<span class="italic">&lt;DISCRIMINATOR_VALUE&gt;</span>")
@PrimaryKeyJoinColumn(name="<span class="italic">&lt;JOIN_COLUMN_NAME&gt;</span>", 
    referencedColumnName = "<span class="italic">&lt;REFERENCED_COLUMN_NAME&gt;</span>")

</pre>
<p><a id="sthref87" name="sthref87"></a><a id="sthref88" name="sthref88"></a><a id="sthref89" name="sthref89"></a>The following figures illustrates the different inheritance strategies.</p>
<div class="figure"><a id="sthref90" name="sthref90"></a>
<p class="titleinfigure">Single Table Inheritance</p>
<img src="img/inheritance_single.png" alt="This figure illustrates entity inheritance in a single table." title="This figure illustrates entity inheritance in a single table." /><br /></div>
<!-- class="figure" -->
<div class="figure"><a id="sthref91" name="sthref91"></a>
<p class="titleinfigure"><a id="sthref92" name="sthref92"></a><a id="sthref93" name="sthref93"></a>Joined Table Inheritance</p>
<img src="img/inheritance_join.png" alt="This figure illustrates a joined subclass inheritance strategy." title="This figure illustrates a joined subclass inheritance strategy." /><br /></div>
<!-- class="figure" -->
<br />
<p>&nbsp;</p>
<img src="img/ngrelt.png" alt="Related task" title="Related task" /><br />
<br />
<a href="task_add_persistence.htm#BABHICAI">Adding persistence to a class</a>
<p>&nbsp;</p>
<img src="img/ngrelc.png" alt="Related concept" title="Related concept" /><br />
<br />
<a href="concept_persistence.htm#BABCAHIC">Understanding Java persistence</a><br /></div>
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