/*
 * Copyright 2002-2012 the original author or authors.
 *
 * 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.springframework.orm.hibernate3;

import java.sql.SQLException;

import org.hibernate.HibernateException;
import org.hibernate.Session;

/**
 * Callback interface for Hibernate code. To be used with {@link HibernateTemplate}'s
 * execution methods, often as anonymous classes within a method implementation.
 * A typical implementation will call {@code Session.load/find/update} to perform
 * some operations on persistent objects. It can also perform direct JDBC operations
 * via Hibernate's {@code Session.connection()}, operating on a JDBC Connection.
 *
 * <p>Note that Hibernate works on unmodified plain Java objects, performing dirty
 * detection via copies made at load time. Returned objects can thus be used outside
 * of an active Hibernate Session without any hassle, e.g. for display in a web GUI.
 * Reassociating such instances with a new Session, e.g. for updates when coming
 * back from the GUI, is straightforward, as the instance has kept its identity.
 * You should care to reassociate them as early as possible though, to avoid having
 * already loaded a version from the database in the same Session.
 *
 * @author Juergen Hoeller
 * @since 1.2
 * @see HibernateTemplate
 * @see HibernateTransactionManager
 */
public interface HibernateCallback<T> {

	/**
	 * Gets called by {@code HibernateTemplate.execute} with an active
	 * Hibernate {@code Session}. Does not need to care about activating
	 * or closing the {@code Session}, or handling transactions.
	 *
	 * <p>If called without a thread-bound Hibernate transaction (initiated
	 * by HibernateTransactionManager), the code will simply get executed on the
	 * underlying JDBC connection with its transactional semantics. If Hibernate
	 * is configured to use a JTA-aware DataSource, the JDBC connection and thus
	 * the callback code will be transactional if a JTA transaction is active.
	 *
	 * <p>Allows for returning a result object created within the callback,
	 * i.e. a domain object or a collection of domain objects.
	 * A thrown custom RuntimeException is treated as an application exception:
	 * It gets propagated to the caller of the template.
	 *
	 * @param session active Hibernate session
	 * @return a result object, or {@code null} if none
	 * @throws HibernateException if thrown by the Hibernate API
	 * @throws SQLException if thrown by Hibernate-exposed JDBC API
	 * @see HibernateTemplate#execute
	 * @see HibernateTemplate#executeFind
	 */
	T doInHibernate(Session session) throws HibernateException, SQLException;

}
