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| <title>Specifying entity inheritance</title> |
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| <meta name="doctitle" content="Specifying entity inheritance" /> |
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| <div class="sect1"><!-- infolevel="all" infotype="General" --> |
| <h1>Specifying entity inheritance</h1> |
| <p><a id="sthref176" name="sthref176"></a><a id="sthref177" name="sthref177"></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> |
| <li> |
| <p>Select the entity in the <span class="gui-object-title">Project Explorer</span>.</p> |
| </li> |
| <li> |
| <p>In the <span class="gui-object-title">JPA Details</span> view, select the <a href="reference026.htm#CACFHGHE">Inheritance</a> information.</p> |
| <div class="figure"><a id="sthref178" name="sthref178"></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>Complete the fields in the <a href="reference026.htm#CACFHGHE">Inheritance</a> area.</p> |
| <p>Use the following table to complete the remaining fields on the tab. See <a href="reference026.htm#CACFHGHE">"Inheritance"</a> for additional details.</p> |
| </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"><INHERITANCE_STRATEGY></span>) |
| @DiscriminatorColumn(name="<span class="italic"><DISCRIMINATOR_COLUMN></span>", |
| discriminatorType=<span class="italic"><DISCRIMINATOR_TYPE></span>) |
| @DiscriminatorValue(value-"<span class="italic"><DISCRIMINATOR_VALUE></span>") |
| @PrimaryKeyJoinColumn(name="<span class="italic"><JOIN_COLUMN_NAME></span>", |
| referencedColumnName = "<span class="italic"><REFERENCED_COLUMN_NAME></span>") |
| |
| </pre> |
| <p><a id="sthref179" name="sthref179"></a><a id="sthref180" name="sthref180"></a><a id="sthref181" name="sthref181"></a>The following figures illustrates the different inheritance strategies.</p> |
| <div class="figure"><a id="sthref182" name="sthref182"></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="sthref183" name="sthref183"></a> |
| <p class="titleinfigure"><a id="sthref184" name="sthref184"></a><a id="sthref185" name="sthref185"></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" --> |
| <a id="sthref186" name="sthref186"></a> |
| <p class="subhead2">Related reference</p> |
| <ul> |
| <li> |
| <p><a href="task_add_persistence.htm#BABHICAI">Adding persistence to a class</a></p> |
| </li> |
| </ul> |
| <a id="sthref187" name="sthref187"></a> |
| <p class="subhead2">Related concepts</p> |
| <ul> |
| <li> |
| <p><a href="concept_persistence.htm#BABCAHIC">Understanding Java persistence</a></p> |
| </li> |
| </ul> |
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