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Cayenne Object Persistence Framework
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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.access;

import org.objectstyle.cayenne.DataObject;
import org.objectstyle.cayenne.DataRow;
import org.objectstyle.cayenne.query.Query;

/**
 * Defines API for a DataContext "delegate" - an object that is temporarily passed control
 * by DataContext at some critical points in the normal flow of execution. A delegate thus
 * can modify the flow, abort an operation, modify the objects participating in an
 * operation, or perform any other tasks it deems necessary. DataContextDelegate is shared
 * by DataContext and its ObjectStore.
 * 
 * @see org.objectstyle.cayenne.access.DataContext
 * @author Mike Kienenberger
 * @author Andrus Adamchik
 * @since 1.1
 */
public interface DataContextDelegate {

    /**
     * Invoked before a GenericSelectQuery is executed. The delegate may
     * modify the GenericSelectQuery by returning a different
     * GenericSelectQuery, or may return null to discard the query.
     * 
     * @return the original or modified GenericSelectQuery or null to
     *         discard the query.
     * @deprecated since 1.2 implement either
     *             {@link #willPerformQuery(DataContext, Query)} or
     *             {@link #willPerformGenericQuery(DataContext, Query)}.
     */
    org.objectstyle.cayenne.query.GenericSelectQuery willPerformSelect(
            DataContext context,
            org.objectstyle.cayenne.query.GenericSelectQuery query);

    /**
     * Invoked before a Query is executed via DataContext.performQuery. The
     * delegate may subsitute the Query with a different one or may return null to discard
     * the query.
     * 
     * @since 1.2
     */
    Query willPerformQuery(DataContext context, Query query);

    /**
     * Invoked before a Query is executed via DataContext.performGenericQuery.
     * The delegate may subsitute the Query with a different one or may return null to
     * discard the query.
     * 
     * @since 1.2
     */
    Query willPerformGenericQuery(DataContext context, Query query);

    /**
     * Invoked by parent DataContext whenever an object change is detected. This can be a
     * change to the object snapshot, or a modification of an "independent" relationship
     * not resulting in a snapshot change. In the later case snapshot argument may be
     * null. If a delegate returns true, ObjectStore will attempt to merge
     * the changes into an object.
     */
    boolean shouldMergeChanges(DataObject object, DataRow snapshotInStore);

    /**
     * Called after a successful merging of external changes to an object. If previosly a
     * delegate returned false from
     * {@link #shouldMergeChanges(DataObject, DataRow)}, this method is not invoked,
     * since changes were not merged.
     */
    void finishedMergeChanges(DataObject object);

    /**
     * Invoked by ObjectStore whenever it is detected that a database row was deleted for
     * object. If a delegate returns true, ObjectStore will change
     * MODIFIED objects to NEW (resulting in recreating the deleted record on next commit)
     * and all other objects - to TRANSIENT. To block this behavior, delegate should
     * return false, and possibly do its own processing.
     * 
     * @param object DataObject that was deleted externally and is still present in the
     *            ObjectStore associated with the delegate.
     */
    boolean shouldProcessDelete(DataObject object);

    /**
     * Called after a successful processing of externally deleted object. If previosly a
     * delegate returned false from
     * {@link #shouldProcessDelete(DataObject)}, this method is not invoked, since no
     * processing was done.
     */
    void finishedProcessDelete(DataObject object);
}