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| <b>Release 2.5</b><br /></font></td> |
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| <div class="refsect1"> |
| <h2 class="refsect1"><font face="arial, helvetica, sans-serif" color="#330099">join-fetch</font></h2> |
| <p>Use <code>eclipselink.join-fetch hint</code> to join attributes in a query.</p> |
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| <p>Use <em>dot notation</em> to access nested attributes. For example, to batch-read an employee's manager's address, use <code>e.manager.address</code>.</p> |
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| <p><strong><br /><span class="refsubsect">Values</span></strong></p> |
| <p><a href="#BABHECAC">Table 4-21</a> describes this query hint's valid values.</p> |
| <div class="tblhruleformalwide"><a id="TLJPA661" name="TLJPA661"></a><a id="sthref621" name="sthref621"></a><a id="BABHECAC" name="BABHECAC"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Table 4-21 Valid Values for eclipselink.join-fetch hint</font></em></strong></p> |
| <table class="HRuleFormalWide" title="Valid Values for eclipselink.join-fetch hint" summary="Valid Values for this query hint" dir="ltr" border="1" width="100%" frame="hsides" rules="rows" cellpadding="3" cellspacing="0"> |
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| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t31"><font face="Arial, Helvetica, sans-serif"><strong>Value</strong></font></th> |
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| <td align="left" id="r2c1-t31" headers="r1c1-t31"> |
| <p>A relationship path expression</p> |
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| <p><strong><br /><span class="refsubsect">Usage</span></strong></p> |
| <p>This hint is similar to <code>eclipselink.<a href="q_batch.htm#batch">batch</a></code>. Subsequent queries of related objects can be optimized in batches instead of being retrieved in one large joined read</p> |
| <p>The <code>eclipselink.join-fetch</code> hint differs from JPQL joining in that it allows multilevel fetch joins.</p> |
| <a id="sthref623" name="sthref623"></a> |
| <p><strong><br /><span class="refsubsect">Examples</span></strong></p> |
| <p><a href="#BABJAJBE">Example 4-42</a> shows how to use this hint in a JPA query.</p> |
| <div class="example"><a id="BABJAJBE" name="BABJAJBE"></a><a id="TLJPA662" name="TLJPA662"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 4-42 Using join-fetch in a JPA Query</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| import org.eclipse.persistence.config.HintValues; |
| import org.eclipse.persistence.config.QueryHints; |
| query.setHint("eclipselink.<strong>join-fetch</strong>", "e.address"); |
| </pre></div> |
| <!-- class="example" --> |
| <p><a href="#BABCAFGJ">Example 4-43</a> shows how to use this hint with the <code>@QueryHint</code> annotation.</p> |
| <div class="example"><a id="BABCAFGJ" name="BABCAFGJ"></a><a id="TLJPA663" name="TLJPA663"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 4-43 Using join-fetch in a @QueryHint Annotation</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| import org.eclipse.persistence.config.HintValues; |
| import org.eclipse.persistence.config.QueryHints; |
| @QueryHint(name=QueryHints.FETCH, value="e.address"); |
| |
| </pre></div> |
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| <p><strong><br /><span class="refsubsect">See Also</span></strong></p> |
| <p>For more information, see:</p> |
| <ul> |
| <li> |
| <p>"EclipseLink" JPA Query Hints<br /> |
| <code><a href="http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/Query_Hints">http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/Query_Hints</a></code></p> |
| </li> |
| <li> |
| <p>EclipseLink Examples<br /> |
| <code><a href="http://wiki.eclipse.org/EclipseLink/Examples/JPA/QueryOptimization">http://wiki.eclipse.org/EclipseLink/Examples/JPA/QueryOptimization</a></code></p> |
| </li> |
| <li> |
| <p>"Optimizing Queries" in <em>Understanding EclipseLink</em>.</p> |
| </li> |
| <li> |
| <p>"Fetch Joins" in the JPA Specification (<code><a href="http://jcp.org/en/jsr/detail?id=317">http://jcp.org/en/jsr/detail?id=317</a></code>)</p> |
| </li> |
| <li> |
| <p><a href="q_batch.htm#batch">"batch"</a></p> |
| </li> |
| <li> |
| <p><a href="q_left-join-fetch.htm#CHDEFDDC">"left-join-fetch"</a></p> |
| </li> |
| <li> |
| <p>"Enhancing Performance" in <em>Solutions Guide for EclispeLink</em></p> |
| </li> |
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