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| Release 2.4</div></td> |
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| <div class="refsect1"> |
| <h2 class="refsect1"><font face="arial, helvetica, sans-serif" color="#330099">@ExistenceChecking</font></h2> |
| <p>Use <code>@ExistenceChecking</code> to specify how EclipseLink should check to determine if an entity is new or exists.</p> |
| <p>On <code>merge()</code> operations, use <code>@ExistenceChecking</code> to specify if EclipseLink uses only the cache to determine if an object exists, or if the object should be read (from the database or cache). By default the object will be read from the database.</p> |
| <a id="sthref118" name="sthref118"></a> |
| <p><strong><br /><span class="refsubsect">Annotation Elements</span></strong></p> |
| <p><a href="#CEGHFAIB">Table 2-20</a> describes this annotation's elements.</p> |
| <div class="tblhruleformalwide"><a id="TLJPA402" name="TLJPA402"></a><a id="sthref119" name="sthref119"></a><a id="CEGHFAIB" name="CEGHFAIB"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Table 2-20 @ExistenceChecking Annotation Elements</font></em></strong></p> |
| <table class="HRuleFormalWide" title="@ExistenceChecking Annotation Elements" summary="This table describes this annotation’s elements." dir="ltr" border="1" width="100%" frame="hsides" rules="rows" cellpadding="3" cellspacing="0"> |
| <col width="23%" /> |
| <col width="*" /> |
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| <thead> |
| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t28"><font face="Arial, Helvetica, sans-serif"><strong>Annotation Element</strong></font></th> |
| <th align="left" valign="bottom" id="r1c2-t28"><font face="Arial, Helvetica, sans-serif"><strong>Description</strong></font></th> |
| <th align="left" valign="bottom" id="r1c3-t28"><font face="Arial, Helvetica, sans-serif"><strong>Default</strong></font></th> |
| </tr> |
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| <tbody> |
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| <td align="left" id="r2c1-t28" headers="r1c1-t28"> |
| <p><code>ExistenceType</code></p> |
| </td> |
| <td align="left" headers="r2c1-t28 r1c2-t28"> |
| <p>(Optional) Set the existence checking type:</p> |
| <ul> |
| <li> |
| <p><code>ASSUME_EXISTENCE</code></p> |
| </li> |
| <li> |
| <p><code>ASSUME_NON_EXISTENCE</code></p> |
| </li> |
| <li> |
| <p><code>CHECK_CHACHE</code></p> |
| </li> |
| <li> |
| <p><code>CHECK_DATABASE</code></p> |
| </li> |
| </ul> |
| </td> |
| <td align="left" headers="r2c1-t28 r1c3-t28"> |
| <p><code>CHECK_CACHE</code></p> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="tblhruleformalwide" --> |
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| <p><strong><br /><span class="refsubsect">Usage</span></strong></p> |
| <p>You can specify <code>@ExistenceChecking</code> on an Entity or MappedSuperclass.</p> |
| <p>EclipseLink supports the following existence checking types:</p> |
| <ul> |
| <li> |
| <p><code>ASSUME_EXISTENCE</code> – If the object's primary key does not include <code>null</code> then it must exist. You may use this option if the application guarantees or does not care about the existence check.</p> |
| </li> |
| <li> |
| <p><code>ASSUME_NON_EXISTENCE</code> – Assume that the object does not exist. You may use this option if the application guarantees or does not care about the existence check. This will always force an <code>INSERT</code> operation.</p> |
| </li> |
| <li> |
| <p><code>CHECK_CHACHE</code> – If the object's primary key does not include <code>null</code> and it is in the cache, then it must exist.</p> |
| </li> |
| <li> |
| <p><code>CHECK_DATABASE</code> – Perform a <code>SELECT</code> on the database.</p> |
| </li> |
| </ul> |
| <a id="sthref121" name="sthref121"></a> |
| <p><strong><br /><span class="refsubsect">Examples</span></strong></p> |
| <p><a href="#CEGDGCHF">Example 2-41</a> shows how to use this annotation.</p> |
| <div class="example"><a id="CEGDGCHF" name="CEGDGCHF"></a><a id="TLJPA54003" name="TLJPA54003"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 2-41 Using @ExistenceChecking Annotation</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| @Entity |
| @Cache(type=CacheType.HARD_WEAK, expiryTimeOfDay=@TimeOfDay(hour=1)) |
| <strong>@ExistenceChecking(ExistenceType.CHECK_DATABASE)</strong> |
| public class Employee implements Serializable { |
| ... |
| } |
| |
| </pre></div> |
| <!-- class="example" --> |
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| <p><strong><br /><span class="refsubsect">See Also</span></strong></p> |
| <p>For more information, see:</p> |
| <ul> |
| <li> |
| <p><a href="a_cache.htm#CHDBBIHE">"@Cache"</a></p> |
| </li> |
| <li> |
| <p>"Enhancing Performance" in <em>Solutions Guide for EclispeLink</em></p> |
| </li> |
| </ul> |
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