/*
* Copyright (c) 2009-2010 Lockheed Martin Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.eurekastreams.commons.hibernate;
import java.util.Collection;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.hibernate.classic.Session;
/**
* SQL Query optimizing class using Hibernate-specific tweaks. The JPA
* EntityManager is injected in.
*/
public class QueryOptimizer
{
/**
* EntityManager to use to get to the Hibernate session.
*/
private EntityManager entityManager;
/**
* Set the entity manager.
*
* @param newEntityManager
* the entity manager.
*/
@PersistenceContext
public void setEntityManager(final EntityManager newEntityManager)
{
this.entityManager = newEntityManager;
}
/**
* Determine the size of the input persisted collection without loading the
* individual entities. This will not work on query results - only
* persistent collections.
*
* @param collection
* The Collection to check the size of.
*
* @return the size of the collection determined without loading it.
*/
public long determineCollectionSize(final Collection<?> collection)
{
if (entityManager == null)
{
throw new NullPointerException("EntityManager is null - needs to be injected.");
}
Session session = (Session) entityManager.getDelegate();
return ((Long) session.createFilter(collection, "select count(*)").list().get(0)).longValue();
}
}