Java Persistence API 1.0 Gotchas

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I've been spending some time checking out the Java Persistence API (JPA) version 1.0 over the past couple of weeks. While the prospect of being able to pick and choose the underlying ORM is enticing, there are several grey areas still not covered by JPA. In fact, some of them can be a very dark grey indeed.

The Missing Information

• No caching strategy
• No custom types
• No one-to-one primary key only associations (known as strategy="foreign", in Hibernate circles)
• No "delete-orphan" cascade type
• No Criteria API
• No table per concrete class inheritance
• No collections of basic types
• No ordered list support (position column)
• No read-only entities
• No dynamic insert and update
• No pessimistic locking

The Work Arounds

  @Column(...)
  @HibernateExtension(...)
  @OpenJPAExtension(...)
  @EclipseLinkExtension(...)
  @UncleTomCobleyExtension(...)
  String myPoorLittleProperty; // Here I am...

The Third Option

package it.syger.jpa;

import javax.persistence.spi.PersistenceProvider;

/**
 * Extension to the original HibernateJpaVendorAdapter class to allow
 * a sub class of the HibernatePersistence class to be used.
 * 
 * @author john.leach
 */
public class HibernateJpaVendorAdapter extends
    org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter {

  private PersistenceProvider provider;

  public void setPersistenceProvider(PersistenceProvider provider) {
    this.provider = provider;
  }

  public PersistenceProvider getPersistenceProvider() {
    return this.provider;
  }
}

package it.syger.jpa;

import java.util.Map;
import javax.persistence.EntityManagerFactory;
import javax.persistence.spi.PersistenceUnitInfo;
import org.hibernate.ejb.Ejb3Configuration;

/**
 * Extension to the original HibernatePersistence class to allow
 * the configured metadata to be programmatically modified before
 * the EntityManagerFactory is created.
 * 
 * This corresponds to a third configuration level, after class
 * annotations, and orm.xml or *.hbm.xml files.
 * 
 * @author john.leach
 */
public class HibernatePersistence extends
    org.hibernate.ejb.HibernatePersistence {

  private HibernateConfigurationBuilder builder;

  public void setHibernateConfigurationBuilder(HibernateConfigurationBuilder builder) {
    this.builder = builder;
  }

  public EntityManagerFactory createEntityManagerFactory(String persistenceUnitName, Map overridenProperties) {
    Ejb3Configuration cfg = new Ejb3Configuration();
    Ejb3Configuration configured = cfg.configure( persistenceUnitName, overridenProperties );
    postConfigure(configured);
    return configured != null ? configured.buildEntityManagerFactory() : null;
  }

  public EntityManagerFactory createContainerEntityManagerFactory(PersistenceUnitInfo info, Map map) {
    Ejb3Configuration cfg = new Ejb3Configuration();
    Ejb3Configuration configured = cfg.configure( info, map );
    postConfigure(configured);
    return configured != null ? configured.buildEntityManagerFactory() : null;
  }

  /**
   * Allow for programmatic modification of the configuration,
   * before the EntityManagerFactory is created.
   * 
   * @param cfg the configuration.
   */
  public void postConfigure(Ejb3Configuration cfg) {
    if (builder != null) {
      builder.setConfiguration(cfg);
      builder.postConfigure();
    }
  }
}

package it.syger.example.domain;

import org.hibernate.ejb.Ejb3Configuration;

import it.syger.jpa.HibernateConfigurationBuilder;

/**
 * Additional modifications, Hibernate specific.
 * 
 * @author john.leach
 */
public class HibernateConfiguration extends HibernateConfigurationBuilder {

  public void postConfigure() {
    configureUser();
  }

  private void configureUser() {
    String className = "it.syger.example.domain.User";
    setPropertyCascade(className, "clients", "all-delete-orphan");
  }
}

Caveat Emptor

The Third Option, Take Two

The Players

• Hibernate has the lion's share of the market (about 54%, or take a look at some graphs), though do remember Disraeli's quote.
• OpenJPA is the open source project based on BEA Kodo.
• Oracle TopLink Essentials is the open source project based on Oracle TopLink and is the Reference Implementation for JPA 1.0.
• EclipseLink is the open source project based on Oracle TopLink, and is (or will be) the Reference Implementation for JPA 2.0.

JPA 2.0 – the Next Generation

The Third Option Code

Nota Bene

Special Thanks

Contacts