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| <title>12. Mapping Limitations</title><link rel="stylesheet" href="css/docbook.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.72.0"><link rel="start" href="manual.html" title="Apache OpenJPA User's Guide"><link rel="up" href="ref_guide_mapping.html" title="Chapter 7. Mapping"><link rel="prev" href="ref_guide_mapping_jpa_map_ex.html" title="11. Examples"><link rel="next" href="ref_guide_mapping_ext.html" title="13. 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">12. |
| Mapping Limitations |
| </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ref_guide_mapping_jpa_map_ex.html">Prev</a> </td><th width="60%" align="center">Chapter 7. |
| Mapping |
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| Mapping Limitations |
| </h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ref_guide_mapping_limits.html#ref_guide_mapping_limits_tpc">12.1. |
| Table Per Class |
| </a></span></dt></dl></div><a class="indexterm" name="d0e26478"></a><p> |
| The following sections outline the limitations OpenJPA places on specific |
| mapping strategies. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="ref_guide_mapping_limits_tpc"></a>12.1. |
| Table Per Class |
| </h3></div></div></div><a class="indexterm" name="d0e26488"></a><p> |
| Table-per-class inheritance mapping has the following limitations: |
| </p><div class="itemizedlist"><ul type="disc"><li><p> |
| You cannot traverse polymorphic relations to non-leaf classes in a |
| table-per-class inheritance hierarchy in queries. |
| </p></li><li><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><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><p> |
| Table-per-class hierarchies impose limitations on eager fetching. See |
| <a 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 href="ref_guide_mapping_ext.html#nonpolymorphic" title="13.2.2. Nonpolymorphic">Section 13.2.2, “ |
| Nonpolymorphic |
| ”</a>. |
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| Mapping Extensions |
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