Create Entity Manager Factory without persistence.

问题:

Is there a way to create the EntityManagerFactory without a persistence unit defined? Can you give all the required properties to create an entity manager factory? I need to create the EntityManagerFactory from the user's specified values at runtime. Updating the persistence.xml and recompiling is not an option.

Currently I am using eclipselink dynamic persistence so i need to create the EntityManagerFactory without a persistence unit defined ? I have groups of runtime entities that need to map single group of entities to different database in runtime and no persistence unit entry is available for this runtime group of entities .

Any idea on how to do this is more than welcomed!

回答1:

Your best option is most likely to access the PersistenceProvider directly and use the EJB container API to create the EntityManagerFactory from a PersistenceUnitInfo.

PersistenceProvider.createContainerEntityManagerFactory()

See, http://www.eclipse.org/eclipselink/api/2.5/org/eclipse/persistence/jpa/PersistenceProvider.html#createContainerEntityManagerFactory%28javax.persistence.spi.PersistenceUnitInfo,%20java.util.Map%29

回答2:

Just seen in the DataNucleus documentation:

import org.datanucleus.metadata.PersistenceUnitMetaData;
import org.datanucleus.api.jpa.JPAEntityManagerFactory;

PersistenceUnitMetaData pumd = new PersistenceUnitMetaData("dynamic-unit", "RESOURCE_LOCAL", null);
pumd.addClassName("org.datanucleus.test.A");
pumd.setExcludeUnlistedClasses();
pumd.addProperty("javax.persistence.jdbc.url", "jdbc:h2:mem:nucleus");
pumd.addProperty("javax.persistence.jdbc.driver", "org.h2.Driver");
pumd.addProperty("javax.persistence.jdbc.user", "sa");
pumd.addProperty("javax.persistence.jdbc.password", "");
pumd.addProperty("datanucleus.autoCreateSchema", "true");

EntityManagerFactory emf = new JPAEntityManagerFactory(pumd, null);

http://www.datanucleus.org/products/accessplatform_3_2/jpa/persistence_unit.html