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| <title>8. Mapping Limitations</title><base href="display"><link rel="stylesheet" type="text/css" href="css/docbook.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="manual.html" title="Apache OpenJPA 3.0 User's Guide"><link rel="up" href="ref_guide_mapping.html" title="Chapter 7. Mapping"><link rel="prev" href="ref_guide_mapping_jpa.html" title="7. Additional JPA Mappings"><link rel="next" href="ref_guide_mapping_ext.html" title="9. Mapping Extensions"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">8. |
| Mapping Limitations |
| </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ref_guide_mapping_jpa.html">Prev</a> </td><th width="60%" align="center">Chapter 7. |
| Mapping |
| </th><td width="20%" align="right"> <a accesskey="n" href="ref_guide_mapping_ext.html">Next</a></td></tr></table><hr></div><div class="section" id="ref_guide_mapping_limits"><div class="titlepage"><div><div><h2 class="title" style="clear: both">8. |
| Mapping Limitations |
| </h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="section"><a href="ref_guide_mapping_limits.html#ref_guide_mapping_limits_tpc">8.1. |
| Table Per Class |
| </a></span></dt></dl></div> |
| |
| <a class="indexterm" name="d5e14917"></a> |
| <p> |
| The following sections outline the limitations OpenJPA places on specific |
| mapping strategies. |
| </p> |
| <div class="section" id="ref_guide_mapping_limits_tpc"><div class="titlepage"><div><div><h3 class="title">8.1. |
| Table Per Class |
| </h3></div></div></div> |
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| <a class="indexterm" name="d5e14923"></a> |
| <p> |
| Table-per-class inheritance mapping has the following limitations: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| <p> |
| You cannot traverse polymorphic relations to non-leaf classes in a |
| table-per-class inheritance hierarchy in queries. |
| </p> |
| </li><li class="listitem"> |
| <p> |
| You cannot map a one-sided polymorphic relation to a non-leaf class in a |
| table-per-class inheritance hierarchy using an inverse foreign key. |
| </p> |
| </li><li class="listitem"> |
| <p> |
| You cannot use an order column in a polymorphic relation to a non-leaf class in |
| a table-per-class inheritance hierarchy mapped with an inverse foreign key. |
| </p> |
| </li><li class="listitem"> |
| <p> |
| Table-per-class hierarchies impose limitations on eager fetching. See |
| <a class="xref" href="ref_guide_perfpack_eager.html#ref_guide_perfpack_eager_consider" title="8.2. Eager Fetching Considerations and Limitations">Section 8.2, “ |
| Eager Fetching Considerations and Limitations |
| ”</a>. |
| </p> |
| </li></ul></div> |
| <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3> |
| <p> |
| Non-polymorphic relations do not suffer from these limitations. You can declare |
| a non-polymorphic relation using the extensions described in |
| <a class="xref" href="ref_guide_mapping_ext.html#nonpolymorphic" title="9.2.2. Nonpolymorphic">Section 9.2.2, “ |
| Nonpolymorphic |
| ”</a>. |
| </p> |
| </div> |
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| </div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ref_guide_mapping_jpa.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ref_guide_mapping.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ref_guide_mapping_ext.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">7. |
| Additional JPA Mappings |
| </td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top"> 9. |
| Mapping Extensions |
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