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<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">Extensible Entities</font></h1>
<p>JPA entities and JAXB beans can be made extensible by adding or modifying mappings externally. There is no need to modify the entity or bean source file nor do you have to redeploy the persistence unit.</p>
<p>Extensible entities are useful in a multi-tenant (or SaaS) architecture where a shared, generic application can be used by multiple clients (tenants). Tenants have private access to their own data, and to data shared with other tenants.</p>
<p>Using extensible entities, you can:</p>
<ul>
<li>
<p>Build an application where some mappings are common to all users and some mappings are user-specific.</p>
</li>
<li>
<p>Add mappings to an application after it is made available to a customer (even post-deployment).</p>
</li>
<li>
<p>Use the same <code>EntityManagerFactory</code> interface to work with data after mappings have changed.</p>
</li>
<li>
<p>Provide an additional source of metadata to be used by an application.</p>
</li>
</ul>
<p>Use the <code>@VirtualAccessMethods</code> annotation to specify that a JPA entity is extensible and use the <code>@XmlVirtualAccessMethods</code> annotation to specify that a JAXB bean is extensible. In both cases, you use virtual properties to specify external mappings. This allows you to modify the mappings without modifying source files and without redeploying the persistence unit.</p>
<p>For information on how to make JPA entities and JAXB beans extensible, see "Making JPA Entities and JAXB Beans Extensible" in <em>Solutions Guide for EclipseLink</em>.</p>
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