001 // Copyright 2004, 2005 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. 014 015 package org.apache.tapestry.components; 016 017 /** 018 * An interface for converting an objects to their primary keys and back. Typically used to 019 * determine how to store a given object as a hidden value when rendering a form. 020 * <p> 021 * This interface is used by the {@link org.apache.tapestry.components.ForBean For component}. When 022 * a primary key converter is available, it is used during the render, and as part of the rewind 023 * phase that processes the form submission. 024 * <p> 025 * During rendering, {@link #getPrimaryKey(Object)} is invoked for each value. This method is 026 * invoked just before the For's body is rendered. The resulting primary key is written into the 027 * client as a hidden form field. 028 * <p> 029 * Likewise, during rewind, {@link #getValue(Object)} is invoked for each key, to get back the same 030 * (or equivalent) object. Again, the method is invoked just before the For's body is rendered. 031 * <p> 032 * The {@link org.apache.tapestry.util.DefaultPrimaryKeyConverter} uses this relationship between a 033 * For component and its primary key converter to track what the current value being rendered or 034 * rewound is. 035 * 036 * @author mb 037 * @since 4.0 038 */ 039 public interface IPrimaryKeyConverter 040 { 041 /** 042 * Returns the primary key of the given value 043 * 044 * @param objValue 045 * the value for which a primary key needs to be extracted 046 * @return the primary key of the value 047 */ 048 Object getPrimaryKey(Object value); 049 050 /** 051 * Returns the value corresponding the given primary key 052 * 053 * @param objPrimaryKey 054 * the primary key for which a value needs to be generated 055 * @return the generated value corresponding to the given primary key 056 */ 057 Object getValue(Object primaryKey); 058 059 }