/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2002,2008 Oracle.  All rights reserved.
 *
 * $Id: SecondaryKeyCreator.java,v 12.7 2008/01/17 05:04:53 mjc Exp $
 */

package com.sleepycat.db;

/**
The interface implemented for extracting single-valued secondary keys from
primary records.
<p>
The key creator object is specified by calling
{@link SecondaryConfig#setKeyCreator SecondaryConfig.setKeyCreator}.
The secondary database configuration is specified when calling
{@link Environment#openSecondaryDatabase Environment.openSecondaryDatabase}.
<p>
For example:
<pre>
    class MyKeyCreator implements SecondaryKeyCreator {
        public boolean createSecondaryKey(SecondaryDatabase secondary,
                                            DatabaseEntry key,
                                            DatabaseEntry data,
                                            DatabaseEntry result)
            throws DatabaseException {
            //
            // DO HERE: Extract the secondary key from the primary key and
            // data, and set the secondary key into the result parameter.
            //
            return true;
        }
    }
    ...
    SecondaryConfig secConfig = new SecondaryConfig();
    secConfig.setKeyCreator(new MyKeyCreator());
    // Now pass secConfig to Environment.openSecondaryDatabase
</pre>
*/
public interface SecondaryKeyCreator {
    /**
    Creates a secondary key entry, given a primary key and data entry.
    <p>
    A secondary key may be derived from the primary key, primary data, or a
    combination of the primary key and data.  For secondary keys that are
    optional, the key creator method may return false and the key/data pair
    will not be indexed.  To ensure the integrity of a secondary database the
    key creator method must always return the same result for a given set of
    input parameters.
    <p>
    @param secondary the database to which the secondary key will be added.
    This parameter is passed for informational purposes but is not commonly
    used.
    <p>
    @param key the primary key entry.  This parameter must not be modified
    by this method.
    <p>
    @param data the primary data entry.  This parameter must not be modified
    by this method.
    <p>
    @param result the secondary key created by this method.
    <p>
    @return true if a key was created, or false to indicate that the key is
    not present.
    <p>
    @throws DatabaseException if an error occurs attempting to create the
    secondary key.
    */
    boolean createSecondaryKey(SecondaryDatabase secondary,
                                      DatabaseEntry key,
                                      DatabaseEntry data,
                                      DatabaseEntry result)
        throws DatabaseException;
}
