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

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{{EclipseLink_TLJPA
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#REDIRECT [[EclipseLink/UserGuide/JPA/2.4/toc]]
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[[Image:Elug_Magnifier.png|Search]][http://www.google.com/cse/home?cx=016171230611334810008:y5kxq4rqd8s&hl=en Search]
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&nbsp;&nbsp;&nbsp;[[Image:Elug_guide_icon.png|Contents]][[EclipseLink/UserGuide/JPA/2.4/toc| Contents]]
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----
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[[EclipseLink/UserGuide/JPA/2.4/a_cache| Previous ]]<span class="previouslink">[[Image:Elug_previous_icon.png|Previous]]</span>
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[[Image:Elug_draft_icon.png|Warning]]Beta Draft: 2012-06-18
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<span id="CEGFEJCH"></span>
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----
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==@CacheIndex==
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Use @CacheIndex to define a cached index. Cache indexes are used only when caching is enabled.
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<span id="sthref40"></span>
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''' '''
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===Annotation Elements===
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[[#BABFJHIC|Table 2-5]] describes this annotation's elements.
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<span id="sthref41"></span><span id="BABFJHIC"></span>
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'''''Table 2-5 @CacheIndex Annotation Elements'''''
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{| class="HRuleFormalWide" dir="ltr" title="@CacheIndex 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-t8" align="left" valign="bottom" | '''Annotation Element'''
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! id="r1c2-t8" align="left" valign="bottom" | '''Description'''
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! id="r1c3-t8" align="left" valign="bottom" | '''Default'''
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|- align="left" valign="top"
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| id="r2c1-t8" headers="r1c1-t8" align="left" |
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<code>columnNames</code>
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| headers="r2c1-t8 r1c2-t8" align="left" |
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(Optional) The set of columns on which to define the index. Not required when annotated on a field/method.
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| headers="r2c1-t8 r1c3-t8" align="left" | <br />
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|- align="left" valign="top"
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| id="r3c1-t8" headers="r1c1-t8" align="left" |
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<code>updateable</code>
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| headers="r3c1-t8 r1c2-t8" align="left" |
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(Optional) Specify if the indexed field is updateable.
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If <code>true</code>, the object will be re-indexed on each update or refresh.
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| headers="r3c1-t8 r1c3-t8" align="left" |
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true
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|}
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<br />
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''' '''
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===Usage===
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A cache index allows <code>singleResult</code> queries to obtain a cache hit when querying on the indexed fields. A <code>resultList</code> query cannot obtain cache hits, as it is unknown if all of the objects are in memory, (unless the cache usage query hint is used).
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The index should be unique. If it is not, the first indexed object will be returned.
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You can use <code>@CacheIndex</code> on an Entity class or on an attribute. The column is defaulted when defined on a attribute.
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''' '''
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===Examples===
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[[#BABEECHH|Example 2-13]] shows an example of using the <code>@CacheIndex</code> annotation.
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<span id="BABEECHH"></span>
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'''''Example 2-13 Using @CacheIndex Annotation'''''
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@Entity
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@CacheIndex(columnNames={"F_NAME", "L_NAME"}, updateable=true)
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public class Employee {
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  @Id
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  private long id;
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  @CacheIndex
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  private String ssn;
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  @Column(name="F_NAME")
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  private String firstName;
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  @Column(name="L_NAME")
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  private String lastName;
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}
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[[#BABIHBCC|Example 2-14]] shows an example of using the <code>&lt;cache-index&gt;</code> XML element in the <code>eclipselink-orm.xml</code> file.
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'''''Example 2-14 Using &lt;cache-index&gt; XML'''''
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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 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-index updateable="true"&gt;
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            &lt;column-name&gt;F_NAME&lt;/column-name&gt;
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            &lt;column-name&gt;L_NAME&lt;/column-name&gt;
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        &lt;/cache-index&gt;
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        &lt;attributes&gt;
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            &lt;id name="id"/&gt;
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            &lt;basic name="ssn"&gt;
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                &lt;cache-index/&gt;
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            &lt;/basic&gt;
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            &lt;basic name="firstName"&gt;
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                &lt;column name="F_NAME"/&gt;
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            &lt;/basic&gt;
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            &lt;basic name="lastName"&gt;
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                &lt;column name="L_NAME"/&gt;
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            &lt;/basic&gt;
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        &lt;/attributes&gt;
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    &lt;/entity&gt;
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&lt;/entity-mappings&gt;
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[[#BABBIAGH|Example 2-15]] shows an example query using a cache index.
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<span id="BABBIAGH"></span>
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'''''Example 2-15 Caching an Index Query'''''
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Query query = em.createQuery("Select e from Employee e where e.firstName = :firstName and e.lastName = :lastName");
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query.setParameter("firstName", "Bob");
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query.setParameter("lastName", "Smith");
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Employee employee = (Employee)query.getSingleResult();
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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/2.4/a_cache|"@Cache"]]
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* "Cache Indexes" <code>http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching/Indexes</code>
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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 Rick Sapir.

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