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Difference between revisions of "EclipseLink/UserGuide/JPA/2.4/a cache"

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{{EclipseLink_TLJPA
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#REDIRECT [[EclipseLink/UserGuide/JPA/2.4/toc]]
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|category=JPA
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|release=2.4.x
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|title=}}
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<span class="metaname">    </span>
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{| class="simple oac_no_warn" width="100%"
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| align="center" valign="top" |
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[http://www.google.com/cse/home?cx=016171230611334810008:y5kxq4rqd8s&hl=en Search]
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| align="center" valign="top" |
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[[EclipseLink/UserGuide/JPA/toc| Contents]]
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----
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{| width="150"
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[[EclipseLink/UserGuide/JPA/a_batchfetch|&lt;- Previous]]
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[[EclipseLink/UserGuide/JPA/a_cacheindex|Next -&gt;]]
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|}
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<span id="CHDBBIHE"></span>
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----
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==@Cache==
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Use <code>@Cache</code>) to configure the EclipseLink object cache. By default, EclipseLink uses a shared object cache to cache all objects. You can configure the caching type and options on a per class basis to allow optimal caching.
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<span id="sthref35"></span>
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''' '''
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===Annotation Elements===
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[[#CDEJJHDG|Table 2-1]] describes this annotation's elements.
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<span id="sthref36"></span><span id="CDEJJHDG"></span>
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'''''Table 2-1 @Cache Annotation Elements'''''
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{| class="HRuleFormalWide" dir="ltr" title="@Cache Annotation Elements" summary="This table describes the list of attributes for this annotation." width="100%" border="1" frame="hsides" rules="rows" cellpadding="3" frame="hsides" rules="rows"
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|- align="left" valign="top"
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! id="r1c1-t2" align="left" valign="bottom" | '''Annotation Element'''
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! id="r1c2-t2" align="left" valign="bottom" | '''Description'''
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! id="r1c3-t2" align="left" valign="bottom" | '''Default'''
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|- align="left" valign="top"
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| id="r2c1-t2" headers="r1c1-t2" align="left" |
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<code>type</code>
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| headers="r2c1-t2 r1c2-t2" align="left" |
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(Optional) Set this attribute to the type (org.eclipse.persistence.annotations.CacheType enumerated type) of the cache that you will be using:
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* <code>FULL</code>
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* <code>WEAK</code>
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* <code>SOFT</code>
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* <code>SOFT_WEAK</code>
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* <code>HARD_WEAK</code>
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* <code>CACHE</code> (not recommended)
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* <code>NONE</code> (not recommended, use <code>shared=false</code> instead)
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You can override this attribute with these persistence unit properties:
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* <code>eclipselink.cache.type.&lt;</code>''<code>ENTITY</code>''<code>&gt;</code>
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* <code>eclipselink.cache.type.default</code>
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| headers="r2c1-t2 r1c3-t2" align="left" |
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<code>CacheType.SOFT_WEAK</code>
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|- align="left" valign="top"
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| id="r3c1-t2" headers="r1c1-t2" align="left" |
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<code>size</code>
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| headers="r3c1-t2 r1c2-t2" align="left" |
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(Optional) Set this attribute to an int value to define the size of cache to use (number of objects).
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| headers="r3c1-t2 r1c3-t2" align="left" |
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<code>100</code>
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|- align="left" valign="top"
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| id="r4c1-t2" headers="r1c1-t2" align="left" |
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<code>shared</code>
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| headers="r4c1-t2 r1c2-t2" align="left" |
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(Optional) Indicate whether cached instances should be in the shared cache or in a client isolated cache (see Isolated Client Session Cache). This allows the shared cache (L2 cache) to be disabled.
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* <code>true</code> —use shared cache for cached instances.
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* <code>false</code>—use client isolated cache for cached instances (no L2 cache).
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| headers="r4c1-t2 r1c3-t2" align="left" |
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<code>true</code>
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|- align="left" valign="top"
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| id="r5c1-t2" headers="r1c1-t2" align="left" |
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<code>expiry</code>
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| headers="r5c1-t2 r1c2-t2" align="left" |
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(Optional) The int value to enable the expiration of the cached instance after a fixed period of time (milliseconds). Queries executed against the cache after this will be forced back to the database for a refreshed copy.
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| headers="r5c1-t2 r1c3-t2" align="left" |
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.<code>-1</code> (no expiry)
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|- align="left" valign="top"
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| id="r6c1-t2" headers="r1c1-t2" align="left" |
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<code>expiryTimeOfDay</code>
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| headers="r6c1-t2 r1c2-t2" align="left" |
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(Optional) Specific time of day (org.eclipse.persistence.annotations.TimeOfDay) when the cached instance will expire. Queries executed against the cache after this will be forced back to the database for a refreshed copy.
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| headers="r6c1-t2 r1c3-t2" align="left" |
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<code>@TimeOfDay(specified=false)</code>
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|- align="left" valign="top"
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| id="r7c1-t2" headers="r1c1-t2" align="left" |
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<code>alwaysRefresh</code>
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| headers="r7c1-t2 r1c2-t2" align="left" |
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(Optional) Set to a boolean value of true to force all queries that go to the database to always refresh the cache
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| headers="r7c1-t2 r1c3-t2" align="left" |
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<code>false</code>
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|- align="left" valign="top"
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| id="r8c1-t2" headers="r1c1-t2" align="left" |
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<code>refreshOnlyIfNewer</code>
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| headers="r8c1-t2 r1c2-t2" align="left" |
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(Optional) Set to a boolean value of true to force all queries that go to the database to refresh the cache only if the data received from the database by a query is newer than the data in the cache (as determined by the optimistic locking field).
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[[Image:Elug_note_icon.png|Note]] '''Note:'''
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* This option only applies if one of the other refreshing options, such as alwaysRefresh, is already enabled.
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* A version field is necessary to apply this feature.
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| headers="r8c1-t2 r1c3-t2" align="left" |
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<code>false</code>
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|- align="left" valign="top"
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| id="r9c1-t2" headers="r1c1-t2" align="left" |
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<code>disableHits</code>
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| headers="r9c1-t2 r1c2-t2" align="left" |
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(Optional) Set to a boolean value of true to force all queries to bypass the cache for hits, but still resolve against the cache for identity. This forces all queries to hit the database.
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| headers="r9c1-t2 r1c3-t2" align="left" |
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<code>false</code>
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|- align="left" valign="top"
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| id="r10c1-t2" headers="r1c1-t2" align="left" |
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<code>coordinationType</code>
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| headers="r10c1-t2 r1c2-t2" align="left" |
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(Optional) Set this attribute to the cache coordination mode (<code>org.eclipse.persistence.annotations.CacheCoordinationType</code> enumerated type).
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<code>CacheCoordinationType.SEND_OBJECT_CHANGES</code>
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|}
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<br />
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<span id="sthref37"></span>
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''' '''
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===Usage===
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You can define the <code>@Cache</code> annotation on the following:
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* <code>@Entity</code>
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* <code>@MappedSuperclass</code>
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* the root of the inheritance hierarchy (if applicable)
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If you define the <code>@Cache</code> annotation on an inheritance subclass, the annotation will be ignored. If you define the <code>@Cache</code> annotation on <code>@Embeddable</code> EclipseLink will throw an exception.
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<span id="sthref38"></span>
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'''Caching in EclipseLink'''
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The EclipseLink cache is an in-memory repository that stores recently read or written objects based on class and primary key values. EclipseLink uses the cache to do the following:
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* Improve performance by holding recently read or written objects and accessing them in-memory to minimize database access.
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* Manage locking and isolation level.
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* Manage object identity.
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For more information about the EclipseLink cache and its default behavior, see:
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* "Caching Overview" <code>http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic JPA Development/Caching/Caching Overview</code>
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* <code>http://wiki.eclipse.org/Introduction_to_Cache_%28ELUG%29</code>
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EclipseLink defines the following entity caching annotations:
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* <code>@Cache</code>
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* <code>[[EclipseLink/UserGuide/JPA/a_timeofday|@TimeOfDay]]</code>
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* <code>[[EclipseLink/UserGuide/JPA/a_existencechecking|@ExistenceChecking]]</code>
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EclipseLink also provides a number of persistence unit properties that you can specify to configure the EclipseLink cache. These properties may compliment or provide an alternative to the usage of annotations.
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For more information, see the following:
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* How to Use the Persistence Unit Properties for Caching <code>http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#How_to_Use_the_Persistence_Unit_Properties_for_Caching</code>
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* What You May Need to Know About Overriding Annotations in JPA <code>http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#What_You_May_Need_to_Know_About_Overriding_Annotations_in_JPA</code>
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* What You May Need to Know About Using EclipseLink JPA Persistence Unit Properties <code>http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#What_You_May_Need_to_Know_About_Using_EclipseLink_JPA_Persistence_Unit_Properties</code>
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<span id="sthref39"></span>
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''' '''
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===Examples===
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[[#CHDEEGCI|Example 2-1]] illustrates an <code>@Cache</code> annotation.
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<span id="CHDEEGCI"></span>
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'''''Example 2-1 Using @Cache Annotation'''''
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...
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@Entity
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@Cache(
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  type=CacheType.SOFT, // Cache everything until the JVM decides memory is low.
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  size=64000  // Use 64,000 as the initial cache size.
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  expiry=36000000,  // 10 minutes
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  coordinationType=CacheCoordinationType.INVALIDATE_CHANGED_OBJECTS  // if cache coordination is used, only send invalidation messages.
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)
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public class Employee {
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  ...
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}
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<span id="sthref40"></span>
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'''''Example 2-2 Using &lt;cache&gt; Element'''''
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&lt;?xml version="1.0"?&gt;
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&lt;entity-mappings
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  xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/orm"
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  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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  xsi:schemaLocation="http://www.eclipse.org/eclipselink/xsds/persistence/orm
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  http://www.eclipse.org/eclipselink/xsds/eclipselink_orm_2_4.xsd"
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  version="2.4"&gt;
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    &lt;entity name="Employee" class="org.acme.Employee" access="FIELD"&gt;
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      &lt;cache type="SOFT" size="64000" expiry="36000000" coordination-type="INVALIDATE_CHANGED_OBJECTS"/&gt;
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    &lt;/entity&gt;
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&lt;/entity-mappings&gt;
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You can also specify caching properties at the persistence unit level (in the <code>persistence.xml</code> file) as shown here:
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<span id="sthref41"></span>
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'''''Example 2-3 Using persistence.xml'''''
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&lt;?xml version="1.0" encoding="UTF-8"?&gt;
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&lt;persistence xmlns="http://java.sun.com/xml/ns/persistence"
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  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_2_0.xsd"
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  version="2.0"&gt;
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    &lt;persistence-unit name="acme" transaction-type="RESOURCE_LOCAL"&gt;
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      &lt;provider&gt;org.eclipse.persistence.jpa.PersistenceProvider&lt;/provider&gt;
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        &lt;exclude-unlisted-classes&gt;false&lt;/exclude-unlisted-classes&gt;
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        &lt;properties&gt;
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          &lt;property name="eclipselink.cache.shared.default" value="false"/&gt;
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          &lt;property name="eclipselink.cache.shared.Employee" value="true"/&gt;
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          &lt;property name="eclipselink.cache.type.Employee" value="SOFT"/&gt;
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          &lt;property name="eclipselink.cache.size.Employee" value="64000"/&gt;
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        &lt;/properties&gt;
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    &lt;/persistence-unit&gt;
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&lt;/persistence&gt;
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<span id="sthref42"></span>
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''' '''
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===See Also===
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For more information, see:
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* [[EclipseLink/UserGuide/JPA/a_existencechecking|"@ExistenceChecking"]]
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* [[EclipseLink/UserGuide/JPA/a_timeofday|"@TimeOfDay"]]
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* "Configuring Caching" <code></code>
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* [[EclipseLink/UserGuide/JPA/a_cacheinterceptor|"@CacheInterceptor"]]
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----
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{| class="simple oac_no_warn" width="100%"
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|-
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{| width="150"
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|-
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[[EclipseLink/UserGuide/JPA/a_batchfetch|&lt;- Previous]]
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| align="center" |
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[[EclipseLink/UserGuide/JPA/a_cacheindex|Next -&gt;]]
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|}
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| width="34%" align="center" |
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[[Image:Eclipselink-logo.gif|150px|EclispeLink]]<br />[http://wiki.eclipse.org/EclipseLink EclipseLink Home]<br />
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{| class="simple oac_no_warn" width="225"
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[http://www.google.com/cse/home?cx=016171230611334810008:y5kxq4rqd8s&hl=en Search]
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| align="center" valign="top" |
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[[EclipseLink/UserGuide/JPA/toc| Contents]]
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|}
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Latest revision as of 12:22, 29 June 2012

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This page was last modified 12:22, 29 June 2012 by Eclipsepedia anonymous user Unnamed Poltroon.

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