/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2009 by Red Hat Inc and/or its affiliates or by
 * third-party contributors as indicated by either @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.property;
import java.io.Serializable;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.Map;

import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.engine.spi.SessionImplementor;

Represents a "back-reference" to the id of a collection owner.  A "back-reference" is pertinent in mapping scenarios
where we have a uni-directional one-to-many association in which only the many side is mapped.  In this case it is
the collection itself which is responsible for the FK value.

In this scenario, the one side has no inherent knowledge of its "owner".  So we introduce a synthetic property into
the one side to represent the association; a so-called back-reference.
Author:
Gavin King, Steve Ebersole/**
 * Represents a "back-reference" to the id of a collection owner.  A "back-reference" is pertinent in mapping scenarios
 * where we have a uni-directional one-to-many association in which only the many side is mapped.  In this case it is
 * the collection itself which is responsible for the FK value.
 * <p/>
 * In this scenario, the one side has no inherent knowledge of its "owner".  So we introduce a synthetic property into
 * the one side to represent the association; a so-called back-reference.
 *
 * @author Gavin King
 * @author Steve Ebersole
 */
public class BackrefPropertyAccessor implements PropertyAccessor {

	private final String propertyName;
	private final String entityName;

	// cache these since they are stateless
	private final BackrefSetter setter; // this one could even be static...
	private final BackrefGetter getter;

	
A placeholder for a property value, indicating that
we don't know the value of the back reference
/**
	 * A placeholder for a property value, indicating that
	 * we don't know the value of the back reference
	 */
	public static final Serializable UNKNOWN = new Serializable() {
		@Override
		public String toString() {
			return "<unknown>";
		}

		public Object readResolve() {
			return UNKNOWN;
		}
	};

	
Constructs a new instance of BackrefPropertyAccessor.
Params:
collectionRole – The collection role which this back ref references.
entityName – The owner's entity name./**
	 * Constructs a new instance of BackrefPropertyAccessor.
	 *
	 * @param collectionRole The collection role which this back ref references.
	 * @param entityName The owner's entity name.
	 */
	public BackrefPropertyAccessor(String collectionRole, String entityName) {
		this.propertyName = collectionRole.substring( entityName.length() + 1 );
		this.entityName = entityName;

		this.setter = new BackrefSetter();
		this.getter = new BackrefGetter();
	}

	@Override
	public Setter getSetter(Class theClass, String propertyName) {
		return setter;
	}

	@Override
	public Getter getGetter(Class theClass, String propertyName) {
		return getter;
	}


	
Internal implementation of a property setter specific to these back-ref properties.
/**
	 * Internal implementation of a property setter specific to these back-ref properties.
	 */
	public static final class BackrefSetter implements Setter {
		@Override
		public Method getMethod() {
			return null;
		}

		@Override
		public String getMethodName() {
			return null;
		}

		@Override
		public void set(Object target, Object value, SessionFactoryImplementor factory) {
			// this page intentionally left blank :)
		}

	}


	
Internal implementation of a property getter specific to these back-ref properties.
/**
	 * Internal implementation of a property getter specific to these back-ref properties.
	 */
	public class BackrefGetter implements Getter {
		@Override
		public Object getForInsert(Object target, Map mergeMap, SessionImplementor session) {
			if ( session == null ) {
				return UNKNOWN;
			}
			else {
				return session.getPersistenceContext().getOwnerId( entityName, propertyName, target, mergeMap );
			}
		}

		@Override
		public Member getMember() {
			return null;
		}

		@Override
		public Object get(Object target) {
			return UNKNOWN;
		}

		@Override
		public Method getMethod() {
			return null;
		}

		@Override
		public String getMethodName() {
			return null;
		}

		@Override
		public Class getReturnType() {
			return Object.class;
		}
	}
}