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    }