001// Copyright 2006, 2008 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.services;
016
017import java.util.Collection;
018
019/**
020 * Defines how changes to fields (within components, within pages) may have their values persisted between requests.
021 * Different implementations store the field values {@linkplain org.apache.tapestry5.internal.services.SessionPersistentFieldStrategy
022 * in the session}, {@linkplain org.apache.tapestry5.internal.services.ClientPersistentFieldStrategy on the client}, or
023 * elsewhere.
024 */
025public interface PersistentFieldStrategy
026{
027    /**
028     * Posts a change of a persistent property.
029     *
030     * @param pageName    the name of the page containing the component
031     * @param componentId the nested id path of the component (or null for the page's root component)
032     * @param fieldName   the name of the field whose persistent value has changed
033     * @param newValue    the new value for the field, possibly null
034     */
035    void postChange(String pageName, String componentId, String fieldName, Object newValue);
036
037    /**
038     * Finds all persistent changes previously stored for the named page (for the current active session or client).
039     */
040    Collection<PersistentFieldChange> gatherFieldChanges(String pageName);
041
042    /**
043     * Discards any saved changes for the name page. There is no expectation that data already gathered from the
044     * strategy and persumably dumped into component instance fields will be affected, but future field access (within
045     * this request or a later one) will show no data for the indicated page.
046     *
047     * @param pageName logical name of page whose field persistent data should be discarded
048     */
049    void discardChanges(String pageName);
050}