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

Revision as of 14:16, 19 June 2012

Beta Draft: 2012-06-18

@CacheIndex

Use @CacheIndex to define a cached index. Cache indexes are used only when caching is enabled.

Annotation Elements

Table 2-5 describes this annotation's elements.

Table 2-5 @CacheIndex Annotation Elements

Usage

A cache index allows singleResult queries to obtain a cache hit when querying on the indexed fields. A resultList 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).

The index should be unique. If it is not, the first indexed object will be returned.

You can use @CacheIndex on an Entity class or on an attribute. The column is defaulted when defined on a attribute.

Examples

Example 2-13 shows an example of using the @CacheIndex annotation.

Example 2-13 Using @CacheIndex Annotation

@Entity
@CacheIndex(columnNames={"F_NAME", "L_NAME"}, updateable=true)
public class Employee {
  @Id
  private long id;
  @CacheIndex
  private String ssn;
  @Column(name="F_NAME")
  private String firstName;
  @Column(name="L_NAME")
  private String lastName;
}

Example 2-14 shows an example of using the <cache-index> XML element in the eclipselink-orm.xml file.

Example 2-14 Using <cache-index> XML

<?xml version="1.0"?>
<entity-mappings
  xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/orm"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.eclipse.org/eclipselink/xsds/persistence/orm http://www.eclipse.org/eclipselink/xsds/eclipselink_orm_2_4.xsd"
  version="2.4">
    <entity name="Employee" class="org.acme.Employee" access="FIELD">
        <cache-index updateable="true">
            <column-name>F_NAME</column-name>
            <column-name>L_NAME</column-name>
        </cache-index>
        <attributes>
            <id name="id"/>
            <basic name="ssn">
                <cache-index/>
            </basic>
            <basic name="firstName">
                <column name="F_NAME"/>
            </basic>
            <basic name="lastName">
                <column name="L_NAME"/>
            </basic>
        </attributes>
    </entity>
</entity-mappings>

Example 2-15 shows an example query using a cache index.

Example 2-15 Caching an Index Query

Query query = em.createQuery("Select e from Employee e where e.firstName = :firstName and e.lastName = :lastName");
query.setParameter("firstName", "Bob");
query.setParameter("lastName", "Smith");
Employee employee = (Employee)query.getSingleResult();

See Also

For more information, see:

• "@Cache"
• "Cache Indexes" http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching/Indexes