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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 2002, 2015 Oracle and/or its affiliates. All rights reserved.
*
*/
package com.sleepycat.persist;
import com.sleepycat.db.DatabaseEntry;
/**
* An adapter that translates between database entries (key, primary key, data)
* and a "value", which may be either the key, primary key, or entity. This
* interface is used to implement a generic index and cursor (BasicIndex and
* BasicCursor). If we didn't use this approach, we would need separate index
* and cursor implementations for each type of value that can be returned. In
* other words, this interface is used to reduce class explosion.
*
* @author Mark Hayes
*/
interface ValueAdapter<V> {
/**
* Creates a DatabaseEntry for the key or returns null if the key is not
* needed.
*/
DatabaseEntry initKey();
/**
* Creates a DatabaseEntry for the primary key or returns null if the
* primary key is not needed.
*/
DatabaseEntry initPKey();
/**
* Creates a DatabaseEntry for the data or returns null if the data is not
* needed. BasicIndex.NO_RETURN_ENTRY may be returned if the data argument
* is required but we don't need it.
*/
DatabaseEntry initData();
/**
* Sets the data array of the given entries to null, based on knowledge of
* which entries are non-null and are not NO_RETURN_ENTRY.
*/
void clearEntries(DatabaseEntry key,
DatabaseEntry pkey,
DatabaseEntry data);
/**
* Returns the appropriate "value" (key, primary key, or entity) using the
* appropriate bindings for that purpose.
*/
V entryToValue(DatabaseEntry key,
DatabaseEntry pkey,
DatabaseEntry data);
/**
* Converts an entity value to a data entry using an entity binding, or
* throws UnsupportedOperationException if this is not appropriate. Called
* by BasicCursor.update.
*/
void valueToData(V value, DatabaseEntry data);
}
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