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/* ====================================================================
 * 
 * The ObjectStyle Group Software License, version 1.1
 * ObjectStyle Group - http://objectstyle.org/
 * 
 * Copyright (c) 2002-2005, Andrei (Andrus) Adamchik and individual authors
 * of the software. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * 3. The end-user documentation included with the redistribution, if any,
 *    must include the following acknowlegement:
 *    "This product includes software developed by independent contributors
 *    and hosted on ObjectStyle Group web site (http://objectstyle.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 * 
 * 4. The names "ObjectStyle Group" and "Cayenne" must not be used to endorse
 *    or promote products derived from this software without prior written
 *    permission. For written permission, email
 *    "andrus at objectstyle dot org".
 * 
 * 5. Products derived from this software may not be called "ObjectStyle"
 *    or "Cayenne", nor may "ObjectStyle" or "Cayenne" appear in their
 *    names without prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE OBJECTSTYLE GROUP OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 * 
 * This software consists of voluntary contributions made by many
 * individuals and hosted on ObjectStyle Group web site.  For more
 * information on the ObjectStyle Group, please see
 * .
 */
package org.objectstyle.cayenne;

import java.io.Serializable;

/**
 * Provides a level of indirection for property value access, most often used for deferred
 * faulting of to-one relationships. A ValueHolder abstracts how a property value is
 * obtained (fetched from DB, etc.), thus simplifying design of an object that uses it.
 * 
 * Here is an example of a bean property implemented using ValueHolder:
 * 
 * 
 *  * protected ValueHolder someProperty;
 * 
 * public SomeClass getSomeProperty() {
 *     return (SomeClass) somePropertyHolder.getValue(SomeClass.class);
 * }
 * 
 * public void setSomeProperty(SomeClass newValue) {
 *     somePropertyHolder.setValue(SomeClass.class, newValue);
 * }
 * 
 * 
 * @since 1.2
 * @author Andrus Adamchik
 */
public interface ValueHolder extends Serializable {

    /**
     * Returns an object stored by this ValueHolder.
     */
    Object getValue() throws CayenneRuntimeException;

    /**
     * Retrieves ValueHolder value without triggering fault resolution.
     */
    Object getValueDirectly() throws CayenneRuntimeException;

    /**
     * Sets an object stored by this ValueHolder.
     * 
     * @param value a new value of the ValueHolder.
     * @return a previous value saved in the ValueHolder.
     */
    Object setValue(Object value) throws CayenneRuntimeException;

    /**
     * Sets ValueHolder vaue without triggering fault resolution.
     */
    Object setValueDirectly(Object value) throws CayenneRuntimeException;

    /**
     * Returns true if the internal value is not yet resolved.
     */
    boolean isFault();

    /**
     * Turns a ValueHolder into a fault.
     */
    void invalidate();
}