2. JPA Extensions

2. JPA Extensions
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2.1. OpenJPAEntityManagerFactory
2.2. OpenJPAEntityManager
2.3. OpenJPAQuery
2.4. Extent
2.5. StoreCache
2.6. QueryResultCache
2.7. FetchPlan
2.8. OpenJPAEntityTransaction
2.9. OpenJPAPersistence

The following sections outline the runtime interfaces you can use to access OpenJPA-specific functionality from JPA. Each interface contains services and convenience methods missing from the JPA specification. OpenJPA strives to use the same naming conventions and API patterns as standard JPA methods in all extensions, so that OpenJPA extension APIs feel as much as possible like standard JPA.

You may have noticed the examples throughout this document using the OpenJPAPersistence.cast methods to cast from standard JPA interfaces to OpenJPA extended interfaces. This is the recommended practice. Some application server vendors may proxy OpenJPA's JPA implementation, preventing a straight cast. OpenJPAPersistence's cast methods work around these proxies.

 
public static OpenJPAEntityManagerFactory cast(EntityManagerFactory emf);
public static OpenJPAEntityManager cast(EntityManager em);
public static OpenJPAQuery cast(Query q);

We provide additional information on the OpenJPAPersistence helper below.

2.1. OpenJPAEntityManagerFactory

The org.apache.openjpa.persistence.OpenJPAEntityManagerFactory interface extends the basic javax.persistence.EntityManagerFactory with OpenJPA-specific features. The OpenJPAEntityManagerFactory offers APIs to access the OpenJPA data and query caches and to perform other OpenJPA-specific operations. See the interface Javadoc for details.

2.2. OpenJPAEntityManager

All OpenJPA EntityManagers implement the org.apache.openjpa.persistence.OpenJPAEntityManager interface. This interface extends the standard javax.persistence.EntityManager. Just as the standard EntityManager is the primary window into JPA services, the OpenJPAEntityManager is the primary window from JPA into OpenJPA-specific functionality. We strongly encourage you to investigate the API extensions this interface contains.

2.3. OpenJPAQuery

OpenJPA extends JPA's standard query functionality with the org.apache.openjpa.persistence.OpenJPAQuery interface. See its Javadoc for details on the convenience methods it provides.

2.4. Extent

An Extent is a logical view of all persistent instances of a given entity class, possibly including subclasses. OpenJPA adds the org.apache.openjpa.persistence.Extent class to the set of Java Persistence APIs. The following code illustrates iterating over all instances of the Magazine entity, without subclasses:

Example 9.2. Using a JPA Extent

import org.apache.openjpa.persistence.*;

...

OpenJPAEntityManager kem = OpenJPAPersistence.cast(em);
Extent<Magazine> mags = kem.createExtent(Magazine.class, false);
for (Magazine m : mags)
    processMagazine(m);

2.5. StoreCache

In addition to the EntityManager object cache the JPA specification provides access to a second level cache via the javax.persistence.Cache interface. OpenJPA provides further extensions via the org.apache.openjpa.persistence.StoreCache interface documented at org.apache.openjpa.persistence.StoreCache. Section 1, “ Data Cache ” has detailed information on OpenJPA's data caching system, including the StoreCache facade.

2.6. QueryResultCache

OpenJPA can cache query results as well as persistent object data. The org.apache.openjpa.persistence.QueryResultCache is an JPA-flavored facade to OpenJPA's internal query cache. See Section 1.4, “ Query Cache ” for details on query caching in OpenJPA.

2.7. FetchPlan

Many of the aforementioned OpenJPA interfaces give you access to an org.apache.openjpa.persistence.FetchPlan instance. The FetchPlan allows you to exercise some control over how objects are fetched from the datastore, including large result set support, custom fetch groups, and lock levels.

OpenJPA goes one step further, extending FetchPlan with org.apache.openjpa.persistence.jdbc.JDBCFetchPlan to add additional JDBC-specific tuning methods. Unless you have customized OpenJPA to use a non-relational back-end (see Section 8, “ Non-Relational Stores ” ), all FetchPlans in OpenJPA implement JDBCFetchPlan, so feel free to cast to this interface.

Fetch plans pass on from parent components to child components. The EntityManagerFactory settings (via your configuration properties) for things like the fetch size, result set type, and custom fetch groups are passed on to the fetch plan of the EntityManagers it produces. The settings of each EntityManager, in turn, are passed on to each Query and Extent it returns. Note that the opposite, however, is not true. Modifying the fetch plan of a Query or Extent does not affect the EntityManager's configuration. Likewise, modifying an EntityManager's configuration does not affect the EntityManagerFactory.

Section 7, “ Fetch Groups ” includes examples using FetchPlans.

2.8. OpenJPAEntityTransaction

org.apache.openjpa.persistence.OpenJPAEntityTransaction extends javax.persistence.EntityTransaction to provide additional transaction-debugging capabilities and some concurrency-related commit and rollback features.

2.9. OpenJPAPersistence

org.apache.openjpa.persistence.OpenJPAPersistence is a static helper class that adds OpenJPA-specific utility methods to javax.persistence.Persistence.