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Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Caching/Query Options"

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==JPA Cache Query Hints==
 
==JPA Cache Query Hints==
JPA 2.0 defines the following query hints to configure a queries interaction with the shared cache:
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JPA 2.0 defines the following query hints to configure a queries interaction with the shared cache.  JPA cache query hints can be set on named or dynamic queries, or set in the properties map passed to the <tt>find()</tt> operation.
 
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Revision as of 14:17, 29 May 2012

EclipseLink JPA

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Elug api package icon.png Key API

Query Cache Options and In-memory Querying

JPA defines standard query hints for configuring how a query interacts with the shared persistence unit cache (L2). EclipseLink also provides some additional query hints for configuring the cache usage.

Entities can be accessed through JPA using either find() or queries. find() will first check the persistence context cache (L1) for the Id, if the object is not found it will check the shared persistence unit cache (L2), if the object is still not found it will access the database. By default all queries will access the database, unless querying by Id or by cache indexed fields. Once the query retrieves the rows from the database, it will resolve each row with the cache. If the object is already in the cache, then the row will be discarded, and the object will be used. If the object is not in the shared cache, then it will be built from the row and put into the shared cache. A copy will also be put in the persistence context cache and returned as the query result.

This is the general process, but it differs if the transaction is dirty. If the transaction is diry then the shared persistence unit cache will be ignored and objects will be built directly into the persistence context cache.

A transaction is considered dirty in the following circumstances:

  • A flush() has written changes to the database.
  • A pessimistic lock query has been executed.
  • An update or delete query has been executed.
  • A native SQL query has been executed.
  • This persistence unit property "eclipselink.transaction.join-existing" is used.
  • The JDBC connection has been unwrapped from the EntityManager.
  • The UnitOfWork API beginEarlyTransaction has been called.

Entities can also be configured to be isolated, or non cacheable, in which case they will never be placed in the shared cache (see Shared, Isolated, Protected, Weak and Read-only Cache).

JPA Cache Query Hints

JPA 2.0 defines the following query hints to configure a queries interaction with the shared cache. JPA cache query hints can be set on named or dynamic queries, or set in the properties map passed to the find() operation.

JPA Cache Query Hints
Hint Description Default Required?
javax.persistence.cache.retrieveMode Configure how the shared cache is accessed.

Valid values are defined in CacheRetrieveMode enum:

  • BYPASS : Ignore the shared cache, and build the object directly into the persistence context cache.
  • USE : Use the shared cache. If the object is already in the shared cache, use the object and discard the database row data.
USE Optional
javax.persistence.cache.storeMode Configure how the shared cache is modified.

Valid values are defined in CacheStoreMode enum:

  • BYPASS : Do not put any object build from the row data into the shared cache.
  • REFRESH : If the object is in the shared cache, refresh its data from the database row data.
  • USE : If the object is not in the shared cache, then build it from the database row data and put it into the shared cache.
USE Optional
Refresh query hint example
Query query = em.createQuery("Select e from Employee e where e.address.city = :city");
query.setHint("javax.persistence.cache.storeMode", "REFRESH");
query.setParameter("city", "Ottawa");
List<Employee> employees = query.getResultList();

EclipseLink Cache Query Hints

EclipseLink defines the following query hints to configure a queries interaction with the shared cache:

EclipseLink Cache Query Hints
Hint Description Default Required?
eclipselink.refresh Configure the query to refresh the objects in both the shared cache and/or the persistence context cache with the database row data. false Optional
eclipselink.refresh.cascade If how refreshing is cascaded to relationships, if the query has been configured to refresh.
  • NoCascading - Do not cascade the refresh to relationships.
  • CascadePrivateParts - Only cascade the refresh to private (orphan-removal) relationships.
  • CascadeAllParts - Cascade the refresh to all relationships.
  • CascadeByMapping - Only cascade the refresh to all relationships that have been configure to cascade refresh.
CascadeByMapping Optional
In-memory query example
Query query = em.createQuery("Select e from Employee e where e.firstName like :firstName and e.lastName like :lastName");
query.setParameter("firstName", "B%");
query.setParameter("lastName", "S%");
List<Employee> employees = query.getResultList();

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Version: 2.4 DRAFT
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