session.java

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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2008, Red Hat Middleware LLC 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 Middleware LLC.
 *
 * 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;

import java.io.Serializable;
import java.sql.Connection;

import org.hibernate.jdbc.Work;
import org.hibernate.stat.SessionStatistics;

/**
 * The main runtime interface between a Java application and Hibernate. This is the
 * central API class abstracting the notion of a persistence service.<br>
 * <br>
 * The lifecycle of a <tt>Session</tt> is bounded by the beginning and end of a logical
 * transaction. (Long transactions might span several database transactions.)<br>
 * <br>
 * The main function of the <tt>Session</tt> is to offer create, read and delete operations
 * for instances of mapped entity classes. Instances may exist in one of three states:<br>
 * <br>
 * <i>transient:</i> never persistent, not associated with any <tt>Session</tt><br>
 * <i>persistent:</i> associated with a unique <tt>Session</tt><br>
 * <i>detached:</i> previously persistent, not associated with any <tt>Session</tt><br>
 * <br>
 * Transient instances may be made persistent by calling <tt>save()</tt>,
 * <tt>persist()</tt> or <tt>saveOrUpdate()</tt>. Persistent instances may be made transient
 * by calling<tt> delete()</tt>. Any instance returned by a <tt>get()</tt> or
 * <tt>load()</tt> method is persistent. Detached instances may be made persistent
 * by calling <tt>update()</tt>, <tt>saveOrUpdate()</tt>, <tt>lock()</tt> or <tt>replicate()</tt>. 
 * The state of a transient or detached instance may also be made persistent as a new
 * persistent instance by calling <tt>merge()</tt>.<br>
 * <br>
 * <tt>save()</tt> and <tt>persist()</tt> result in an SQL <tt>INSERT</tt>, <tt>delete()</tt>
 * in an SQL <tt>DELETE</tt> and <tt>update()</tt> or <tt>merge()</tt> in an SQL <tt>UPDATE</tt>. 
 * Changes to <i>persistent</i> instances are detected at flush time and also result in an SQL
 * <tt>UPDATE</tt>. <tt>saveOrUpdate()</tt> and <tt>replicate()</tt> result in either an
 * <tt>INSERT</tt> or an <tt>UPDATE</tt>.<br>
 * <br>
 * It is not intended that implementors be threadsafe. Instead each thread/transaction
 * should obtain its own instance from a <tt>SessionFactory</tt>.<br>
 * <br>
 * A <tt>Session</tt> instance is serializable if its persistent classes are serializable.<br>
 * <br>
 * A typical transaction should use the following idiom:
 * <pre>
 * Session sess = factory.openSession();
 * Transaction tx;
 * try {
 *     tx = sess.beginTransaction();
 *     //do some work
 *     ...
 *     tx.commit();
 * }
 * catch (Exception e) {
 *     if (tx!=null) tx.rollback();
 *     throw e;
 * }
 * finally {
 *     sess.close();
 * }
 * </pre>
 * <br>
 * If the <tt>Session</tt> throws an exception, the transaction must be rolled back
 * and the session discarded. The internal state of the <tt>Session</tt> might not
 * be consistent with the database after the exception occurs.
 *
 * @see SessionFactory
 * @author Gavin King
 */
public interface Session extends Serializable {

	/**
	 * Retrieve the entity mode in effect for this session.
	 *
	 * @return The entity mode for this session.
	 */
	public EntityMode getEntityMode();

	/**
	 * Starts a new Session with the given entity mode in effect. This secondary
	 * Session inherits the connection, transaction, and other context
	 * information from the primary Session. It doesn't need to be flushed
	 * or closed by the developer.
	 * 
	 * @param entityMode The entity mode to use for the new session.
	 * @return The new session
	 */
	public Session getSession(EntityMode entityMode);

	/**
	 * Force this session to flush. Must be called at the end of a
	 * unit of work, before commiting the transaction and closing the
	 * session (depending on {@link #setFlushMode flush-mode},
	 * {@link Transaction#commit()} calls this method).
	 * <p/>
	 * <i>Flushing</i> is the process of synchronizing the underlying persistent
	 * store with persistable state held in memory.
	 *
	 * @throws HibernateException Indicates problems flushing the session or
	 * talking to the database.
	 */
	public void flush() throws HibernateException;

	/**
	 * Set the flush mode for this session.
	 * <p/>
	 * The flush mode determines the points at which the session is flushed.
	 * <i>Flushing</i> is the process of synchronizing the underlying persistent
	 * store with persistable state held in memory.
	 * <p/>
	 * For a logically "read only" session, it is reasonable to set the session's
	 * flush mode to {@link FlushMode#MANUAL} at the start of the session (in
	 * order to achieve some extra performance).
	 *
	 * @param flushMode the new flush mode
	 * @see FlushMode
	 */
	public void setFlushMode(FlushMode flushMode);

	/**
	 * Get the current flush mode for this session.
	 *
	 * @return The flush mode
	 */
	public FlushMode getFlushMode();

	/**
	 * Set the cache mode.
	 * <p/>
	 * Cache mode determines the manner in which this session can interact with
	 * the second level cache.
	 *
	 * @param cacheMode The new cache mode.
	 */
	public void setCacheMode(CacheMode cacheMode);

	/**
	 * Get the current cache mode.
	 *
	 * @return The current cache mode.
	 */
	public CacheMode getCacheMode();

	/**
	 * Get the session factory which created this session.
	 *
	 * @return The session factory.
	 * @see SessionFactory

	 */
	public SessionFactory getSessionFactory();

	/**
	 * Get the JDBC connection of this Session.<br>
	 * <br>
	 * If the session is using aggressive collection release (as in a
	 * CMT environment), it is the application's responsibility to
	 * close the connection returned by this call. Otherwise, the
	 * application should not close the connection.
	 *
	 * @return the JDBC connection in use by the <tt>Session</tt>
	 * @throws HibernateException if the <tt>Session</tt> is disconnected
	 * @deprecated (scheduled for removal in 4.x).  Replacement depends on need; for doing direct JDBC stuff use
	 * {@link #doWork}; for opening a 'temporary Session' use (TBD).
	 */
	public Connection connection() throws HibernateException;

	/**
	 * End the session by releasing the JDBC connection and cleaning up.  It is
	 * not strictly necessary to close the session but you must at least
	 * {@link #disconnect()} it.
	 *
	 * @return the connection provided by the application or null.
	 * @throws HibernateException Indicates problems cleaning up.
	 */
	public Connection close() throws HibernateException;

	/**
	 * Cancel the execution of the current query.
	 * <p/>
	 * This is the sole method on session which may be safely called from
	 * another thread.
	 *
	 * @throws HibernateException There was a problem canceling the query
	 */
	public void cancelQuery() throws HibernateException;

	/**
	 * Check if the session is still open.
	 *
	 * @return boolean
	 */
	public boolean isOpen();

	/**
	 * Check if the session is currently connected.
	 *
	 * @return boolean
	 */
	public boolean isConnected();

	/**
	 * Does this session contain any changes which must be synchronized with
	 * the database?  In other words, would any DML operations be executed if
	 * we flushed this session?
	 *
	 * @return True if the session contains pending changes; false otherwise.
	 * @throws HibernateException could not perform dirtying checking
	 */
	public boolean isDirty() throws HibernateException;

	/**
	 * Return the identifier value of the given entity as associated with this
	 * session.  An exception is thrown if the given entity instance is transient
	 * or detached in relation to this session.
	 *
	 * @param object a persistent instance
	 * @return the identifier
	 * @throws TransientObjectException if the instance is transient or associated with
	 * a different session
	 */
	public Serializable getIdentifier(Object object) throws HibernateException;

	/**
	 * Check if this instance is associated with this <tt>Session</tt>.
	 *
	 * @param object an instance of a persistent class
	 * @return true if the given instance is associated with this <tt>Session</tt>
	 */
	public boolean contains(Object object);

	/**
	 * Remove this instance from the session cache. Changes to the instance will
	 * not be synchronized with the database. This operation cascades to associated
	 * instances if the association is mapped with <tt>cascade="evict"</tt>.
	 *
	 * @param object a persistent instance
	 * @throws HibernateException
	 */
	public void evict(Object object) throws HibernateException;

	/**
	 * Return the persistent instance of the given entity class with the given identifier,
	 * obtaining the specified lock mode, assuming the instance exists.
	 *
	 * @param theClass a persistent class
	 * @param id a valid identifier of an existing persistent instance of the class
	 * @param lockMode the lock level
	 * @return the persistent instance or proxy
	 * @throws HibernateException
	 */