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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2012, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.event.internal;

import java.io.Serializable;

import org.hibernate.HibernateException;
import org.hibernate.cache.spi.access.NaturalIdRegionAccessStrategy;
import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.event.spi.ResolveNaturalIdEvent;
import org.hibernate.event.spi.ResolveNaturalIdEventListener;
import org.hibernate.internal.CoreLogging;
import org.hibernate.internal.CoreMessageLogger;
import org.hibernate.persister.entity.EntityPersister;
import org.hibernate.pretty.MessageHelper;

/**
 * Defines the default load event listeners used by hibernate for loading entities
 * in response to generated load events.
 * 
 * @author Eric Dalquist
 * @author Steve Ebersole
 */
public class DefaultResolveNaturalIdEventListener
		extends AbstractLockUpgradeEventListener
		implements ResolveNaturalIdEventListener {

	public static final Object REMOVED_ENTITY_MARKER = new Object();
	public static final Object INCONSISTENT_RTN_CLASS_MARKER = new Object();

	private static final CoreMessageLogger LOG = CoreLogging.messageLogger( DefaultResolveNaturalIdEventListener.class );

	@Override
	public void onResolveNaturalId(ResolveNaturalIdEvent event) throws HibernateException {
		final Serializable entityId = resolveNaturalId( event );
		event.setEntityId( entityId );
	}

	/**
	 * Coordinates the efforts to load a given entity. First, an attempt is
	 * made to load the entity from the session-level cache. If not found there,
	 * an attempt is made to locate it in second-level cache. Lastly, an
	 * attempt is made to load it directly from the datasource.
	 * 
	 * @param event The load event
	 *
	 * @return The loaded entity, or null.
	 */
	protected Serializable resolveNaturalId(final ResolveNaturalIdEvent event) {
		final EntityPersister persister = event.getEntityPersister();

		final boolean traceEnabled = LOG.isTraceEnabled();
		if ( traceEnabled )
			LOG.tracev( "Attempting to resolve: {0}",
					MessageHelper.infoString( persister, event.getNaturalIdValues(), event.getSession().getFactory() ) );

		Serializable entityId = resolveFromCache( event );
		if ( entityId != null ) {
			if ( traceEnabled )
				LOG.tracev( "Resolved object in cache: {0}",
						MessageHelper.infoString( persister, event.getNaturalIdValues(), event.getSession().getFactory() ) );
			return entityId;
		}

		if ( traceEnabled )
			LOG.tracev( "Object not resolved in any cache: {0}",
					MessageHelper.infoString( persister, event.getNaturalIdValues(), event.getSession().getFactory() ) );

		return loadFromDatasource( event );
	}

	/**
	 * Attempts to resolve the entity id corresponding to the event's natural id values from the session
	 * 
	 * @param event The load event
	 *
	 * @return The entity from the cache, or null.
	 */
	protected Serializable resolveFromCache(final ResolveNaturalIdEvent event) {
		return event.getSession().getPersistenceContext().getNaturalIdHelper().findCachedNaturalIdResolution(
				event.getEntityPersister(),
				event.getOrderedNaturalIdValues()
		);
	}

	/**
	 * Performs the process of loading an entity from the configured
	 * underlying datasource.
	 * 
	 * @param event The load event
	 *
	 * @return The object loaded from the datasource, or null if not found.
	 */
	protected Serializable loadFromDatasource(final ResolveNaturalIdEvent event) {
		final SessionFactoryImplementor factory = event.getSession().getFactory();
		final boolean stats = factory.getStatistics().isStatisticsEnabled();
		long startTime = 0;
		if ( stats ) {
			startTime = System.currentTimeMillis();
		}
		
		final Serializable pk = event.getEntityPersister().loadEntityIdByNaturalId(
				event.getOrderedNaturalIdValues(),
				event.getLockOptions(),
				event.getSession()
		);
		
		if ( stats ) {
			final NaturalIdRegionAccessStrategy naturalIdCacheAccessStrategy = event.getEntityPersister().getNaturalIdCacheAccessStrategy();
			final String regionName = naturalIdCacheAccessStrategy == null ? null : naturalIdCacheAccessStrategy.getRegion().getName();
			
			factory.getStatisticsImplementor().naturalIdQueryExecuted(
					regionName,
					System.currentTimeMillis() - startTime );
		}
		
		//PK can be null if the entity doesn't exist
		if (pk != null) {
			event.getSession().getPersistenceContext().getNaturalIdHelper().cacheNaturalIdCrossReferenceFromLoad(
					event.getEntityPersister(),
					pk,
					event.getOrderedNaturalIdValues()
			);
		}
		
		return pk;
	}
}