1/*- 2 * See the file LICENSE for redistribution information. 3 * 4 * Copyright (c) 2002-2009 Oracle. All rights reserved. 5 * 6 * $Id$ 7 */ 8 9package com.sleepycat.persist; 10 11import com.sleepycat.db.DatabaseEntry; 12 13/** 14 * An adapter that translates between database entries (key, primary key, data) 15 * and a "value", which may be either the key, primary key, or entity. This 16 * interface is used to implement a generic index and cursor (BasicIndex and 17 * BasicCursor). If we didn't use this approach, we would need separate index 18 * and cursor implementations for each type of value that can be returned. In 19 * other words, this interface is used to reduce class explosion. 20 * 21 * @author Mark Hayes 22 */ 23interface ValueAdapter<V> { 24 25 /** 26 * Creates a DatabaseEntry for the key or returns null if the key is not 27 * needed. 28 */ 29 DatabaseEntry initKey(); 30 31 /** 32 * Creates a DatabaseEntry for the primary key or returns null if the 33 * primary key is not needed. 34 */ 35 DatabaseEntry initPKey(); 36 37 /** 38 * Creates a DatabaseEntry for the data or returns null if the data is not 39 * needed. BasicIndex.NO_RETURN_ENTRY may be returned if the data argument 40 * is required but we don't need it. 41 */ 42 DatabaseEntry initData(); 43 44 /** 45 * Sets the data array of the given entries to null, based on knowledge of 46 * which entries are non-null and are not NO_RETURN_ENTRY. 47 */ 48 void clearEntries(DatabaseEntry key, 49 DatabaseEntry pkey, 50 DatabaseEntry data); 51 52 /** 53 * Returns the appropriate "value" (key, primary key, or entity) using the 54 * appropriate bindings for that purpose. 55 */ 56 V entryToValue(DatabaseEntry key, 57 DatabaseEntry pkey, 58 DatabaseEntry data); 59 60 /** 61 * Converts an entity value to a data entry using an entity binding, or 62 * throws UnsupportedOperationException if this is not appropriate. Called 63 * by BasicCursor.update. 64 */ 65 void valueToData(V value, DatabaseEntry data); 66} 67