001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *  
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *  
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License. 
018 *  
019 */
020package org.apache.directory.server.xdbm.search;
021
022
023import org.apache.directory.api.ldap.model.entry.Entry;
024import org.apache.directory.api.ldap.model.exception.LdapException;
025import org.apache.directory.api.ldap.model.filter.ExprNode;
026import org.apache.directory.server.core.api.partition.PartitionTxn;
027import org.apache.directory.server.xdbm.IndexEntry;
028
029
030/**
031 * Evaluates candidate entries to see if they match a filter expression.
032 *
033 * Evaluators contain various overloads to the evaluate method.  Often a
034 * developer working in this region of the code may wonder when to use one
035 * override verses another.  The overload taking an IndexEntry argument is
036 * specifically suited for use when there is the possibility of multiple entry
037 * lookups from the master table.  If the same candidate in the form of an
038 * IndexEntry is evaluated more then this overload is more efficient since it
039 * stores the looked up entry in the IndexEntry preventing multiple lookups.
040 *
041 * If the index entry is already populated with an entry object, and some
042 * evaluation is required then it is preferrable to use the overload that
043 * takes a Long id instead.  Likewise if it is known in advance that the
044 * expression is a leaf node built on an indexed attribute then the overload
045 * with the Long id argument is also preferrable unless an IndexEntry already
046 * exists in which case it makes no difference.
047 *
048 * The overload taking the ServerEntry itself is a last resort option and ok
049 * to use when it is known that no index exists for the attributes of
050 * Evaluators based on leaf expressions.
051 * 
052 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
053 */
054public interface Evaluator<N extends ExprNode>
055{
056    /**
057     * Evaluates a candidate to determine if a filter expression selects it.
058     * If an IndexEntry does has a null reference to the entry object, this
059     * Evaluator may set it if it has to access the full entry within the
060     * master table of the store.  Subsequent evaluations on the IndexEntry
061     * then need not access the store to retreive the entry if they need to
062     * access it's attributes.
063     * 
064     * @param partitionTxn The transaction to use
065     * @param entry the index record of the entry to evaluate
066     * @return true if filter selects the candidate false otherwise
067     * @throws LdapException if there are faults during evaluation
068     */
069    boolean evaluate( PartitionTxn partitionTxn, IndexEntry<?, String> entry ) throws LdapException;
070
071
072    /**
073     * Evaluates whether or not a candidate, satisfies the expression
074     * associated with this Evaluator .
075     *
076     * @param entry the candidate entry
077     * @return true if filter selects the candidate false otherwise
078     * @throws LdapException if there are faults during evaluation
079     */
080    boolean evaluate( Entry entry ) throws LdapException;
081
082
083    /**
084     * Gets the expression used by this expression Evaluator.
085     *
086     * @return the AST for the expression
087     */
088    N getExpression();
089
090
091    /**
092     * Pretty-print an Evaluator
093     * @param tabs The tabs to add before the evaluator
094     * @return The pretty-printed evaluator and its descendants
095     */
096    String toString( String tabs );
097}