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| <title>9. Key Join 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_map_keycols.html" title="8. Key Columns"><link rel="next" href="ref_guide_mapping_jpa_map_embedkey.html" title="10. Key Embedded Mapping"></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">9. Key Join Columns</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ref_guide_mapping_jpa_map_keycols.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_embedkey.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_keyjoincols"></a>9. Key Join Columns</h2></div></div></div><a class="indexterm" name="d0e27505"></a><p> | |
| Key join columns are equivalent to standard JPA | |
| join columns, except that they represent a join to a map key entity rather than a direct relation. You represent | |
| a key join column with OpenJPA's | |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/jdbc/KeyJoinColumn.html" target="_top"> | |
| <code class="classname">org.apache.openjpa.persistence.jdbc.KeyJoinColumn</code></a> annotation. To declare a compound join, enclose an | |
| array of <code class="classname">KeyJoinColumn</code>s in the | |
| <a xmlns:xlink="http://www.w3.org/1999/xlink" href="../javadoc/org/apache/openjpa/persistence/jdbc/KeyJoinColumns.html" target="_top"> | |
| <code class="classname">org.apache.openjpa.persistence.jdbc.KeyJoinColumns</code> | |
| </a> annotation. | |
| </p><p> | |
| A <code class="classname">KeyJoinColumn</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">JoinColumn</code>. Like <code class="classname">XJoinColumn</code>s above, | |
| <code class="classname">KeyJoinColumn</code>s can reference a linked field | |
| rather than a static linked column. Otherwise, the <code class="classname">KeyJoinColumn</code> | |
| and standard <code class="classname">JoinColumn</code> annotations are equivalent. See | |
| <a href="jpa_overview_mapping_field.html#jpa_overview_mapping_rel" title="8.4. Direct Relations">Section 8.4, “ | |
| Direct Relations | |
| ”</a> in the JPA | |
| Overview for a review of the <code class="classname">JoinColumn</code> annotation. | |
| </p></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_map_keycols.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_jpa_map_embedkey.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">8. Key Columns </td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top"> 10. Key Embedded Mapping</td></tr></table></div></body></html> |