org.hibernate.property.BackrefPropertyAccessor Maven / Gradle / Ivy
/*
* 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
* @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
*/
public static final Serializable UNKNOWN = new Serializable() {
public String toString() {
return "";
}
public Object readResolve() {
return UNKNOWN;
}
};
/**
* 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();
}
/**
* {@inheritDoc}
*/
public Setter getSetter(Class theClass, String propertyName) {
return setter;
}
/**
* {@inheritDoc}
*/
public Getter getGetter(Class theClass, String propertyName) {
return getter;
}
/**
* Internal implementation of a property setter specific to these back-ref properties.
*/
public static final class BackrefSetter implements Setter {
/**
* {@inheritDoc}
*/
public Method getMethod() {
return null;
}
/**
* {@inheritDoc}
*/
public String getMethodName() {
return null;
}
/**
* {@inheritDoc}
*/
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.
*/
public class BackrefGetter implements Getter {
/**
* {@inheritDoc}
*/
public Object getForInsert(Object target, Map mergeMap, SessionImplementor session) {
if ( session == null ) {
return UNKNOWN;
}
else {
return session.getPersistenceContext().getOwnerId( entityName, propertyName, target, mergeMap );
}
}
/**
* {@inheritDoc}
*/
public Member getMember() {
return null;
}
/**
* {@inheritDoc}
*/
public Object get(Object target) {
return UNKNOWN;
}
/**
* {@inheritDoc}
*/
public Method getMethod() {
return null;
}
/**
* {@inheritDoc}
*/
public String getMethodName() {
return null;
}
/**
* {@inheritDoc}
*/
public Class getReturnType() {
return Object.class;
}
}
}