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| <title>8. Key Columns</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 1.2 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_jpa_map_keyjoincols.html" title="9. Key Join Columns"></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. Key Columns</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_jpa_map_keyjoincols.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ref_guide_mapping_jpa_map_keycols"></a>8. Key Columns</h2></div></div></div><a class="indexterm" name="d0e27456"></a><p> | |
| Key columns serve the same role for map keys as the element | |
| columns described in | |
| <a href="">???</a> serve for | |
| collection elements. OpenJPA's | |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/jdbc/KeyColumn.html" target="_top"> | |
| <code class="classname">org.apache.openjpa.persistence.jdbc.KeyColumn</code> | |
| </a> annotation represents a map key. To map custom | |
| multi-column keys, use the | |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/jdbc/KeyColumns.html" target="_top"> | |
| <code class="classname">org.apache.openjpa.persistence.jdbc.KeyColumns</code> | |
| </a> annotation, whose value is an array of <code class="classname">KeyColumn</code>s. | |
| </p><p> | |
| A <code class="classname">KeyColumn</code> always resides in | |
| a container table, so it does not have the <code class="literal">table</code> | |
| property of a standard <code class="classname">Column</code>. Otherwise, the | |
| <code class="classname">KeyColumn</code> and standard <code class="classname">Column</code> | |
| annotations are equivalent. See | |
| <a href="jpa_overview_mapping_column.html" title="3. Column">Section 3, “ | |
| Column | |
| ”</a> in the JPA | |
| Overview for a review of the <code class="classname">Column</code> annotation. | |
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| Additional JPA Mappings | |
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